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LIFE: ITS NATURE,

ORIGIN AND MAINTENANCE

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LIFE : ITS NATURE, ORIGIN AND

MAINTENANCE AN ADDRESS
DELIVERED TO THE BRITISH ASSOCI-
ATION FOR THE ADVANCEMENT
OF SCIENCE, AT ITS MEETING AT
DUNDEE IN SEPTEMBER, 1912

BY

E. A. SCHAFER, LL.D., D.Sc., M.D., F.R.S.

PROFESSOR OF PHYSIOLOGY IN EDINBURGH

LONGMANS, GREEN AND CO.

39 PATERNOSTER ROW, LONDON
NEW YORK, BOMBAY AND CALCUTTA

1912

PREFACE

IN the following Essay, which formed the Presidential Address to the
British Association at its meeting this year in Dundee, I have tried to
indicate in clear language the general trend of modern bio-chemical
inquiries regarding the nature and origin of living material and the
manner in which the life of multicellular organisms, especially that of
the higher animals and man, is maintained. I have also stated the
conclusions which it appears to me may legitimately be drawn from the
result of those inquiries, without ignoring or minimising such difficulties
as these conclusions present.

There is, it may be admitted, nothing new in the idea that living
matter must at some time or another have been formed from lifeless
material, for in spite of the dictum omne mvum e vivo, there was certainly
a period in the history of the earth when our planet could have supported
no kind of life, as we understand the word ; there can, therefore, exist
no difference of opinion upon this point among scientific thinkers. Nor
is it the first time that the possibility of the synthetic production of
living substance in the laboratory has been suggested. But only those
who are ignorant of the progress which bio-chemistry has made in recent
years would be bold enough to affirm that the subject is not more
advanced than in the days of Tyndall and of Huxley, who showed the
true scientific instinct in affirming a belief in the original formation of
life from lifeless material and in hinting at ,the possibility of its eventual
synthesis, although there was then far less foundation upon which to base
such an opinion than we of the present day possess. The investigations
of Fischer, of Abderhalden, of Hopkins, and of others too numerous to
mention, have thrown a flood of light upon the constitution of the mate-
rials of which living substance is composed ; and, in particular, the epoch-
making researches of Kossel into the chemical composition of nuclear
substance which in certain forms may be regarded as the simplest type
of living matter, while it is certainly the fons et origo of all active
chemical processes within most cells have shown how much less com-
plex in chemical nature this substance may be than physiologists were
a few years ago accustomed to regard it. On this and other grounds it
has lately been independently suggested by Professor Minchin that the
first living material originally took the form, not of what is commonly

5

6 PEEPACE

termed protoplasm, but of nuclear matter or chromatin : a suggestion
which appears by no means improbable.

If the honoured names of Charles Darwin, Ernst Hackel, and August
Weismann are not found in the following pages, it is because exigencies
of space and time rendered it necessary to deal mainly with the more
modern developments of this chapter of evolutionary history. For other
but not less cogent reasons all metaphysical speculations on the subjects
dealt with have been avoided. The study of Natural Knowledge, as the
Eoyal Society still quaintly describes in its title the investigation of the
phenomena of Nature, is never properly advanced if mixed up with the
' supernatural ' or if metaphysics is appealed to for the explanation of
scientific problems which cannot at once be solved by ordinary scientific
methods ; and it behoves us to eliminate all considerations involving the
intervention of supernatural agencies just as much in connection with
scientific inquiries into the nature and origin of life as with all other
matters which are properly the subject of scientific investigation. This is
not materialism, but common sense.

The first part of the subject of this Address is dealt with at consider-
able length and in a strictly scientific spirit by Le Dantec in ' The Nature
and Origin of Life ' ; as well as by Dastre in the book mentioned on
the next page. To works such as these the reader is referred for the
numerous details which it is impossible to include within the limits of
a short Essay.

UNIVERSITY, EDINBURGH,
October, 1912.

LIFE: ITS NATURE, ORIGIN AND MAINTENANCE

EVERYBODY knows, or thinks he knows, what life is ; at least, we are all
acquainted with its ordinary, obvious manifestations. It would, therefore,

seem that it should not be difficult to find an exact
definition. The quest has nevertheless baffled the
most acute thinkers. Herbert Spencer devoted two chapters of his
' Principles of Biology ' to the discussion of the attempts at definition
which had up to that date been proposed, and himself suggested another.
But at the end of it all he is constrained to admit that no expression had
been found which would embrace all the known manifestations of animate,
and at the same time exclude those of admittedly inanimate, objects.

The ordinary dictionary definition of life is 'the state of living.'
Dastre, following Claude Bernard, defines it as ' the sum total of
the phenomena common to all living beings.' Both of these definitions
are, however, of the same character as Sidney Smith's definition of an
archdeacon as ' a person who performs archidiaconal functions.' I am
not myself proposing to take up your time by attempting to grapple with a
task which has proved too great for the intellectual giants of philosophy,
and I have the less disposition to do so because recent advances in
knowledge have suggested the probability that the dividing line between
animate and inanimate matter is less sharp than it has hitherto been
regarded, so that the difficulty of finding an inclusive definition is corre-
spondingly increased.

As a mere word ' life ' is interesting in the fact that it is one of those
abstract 'terms which has no direct antithesis ; although probably most
persons would regard ' death ' in that light. A little consideration will show
that this is not the case. ' Death ' implies the pre-existence of ' life ' ;
there are physiological grounds for regarding death as a phenomenon of
life it is the completion, the last act of life. We cannot speak of a non-
living object a& possessing death in the sense that we speak of a living object
as possessing life. The adjective ' dead ' is, it is true, applied in a popular
sense antithetically to objects which have never possessed life ; as in the
proverbial expression ' as dead as a door-nail.' But in the strict sense
such application is not justifiable, since the use of the terms dead and
living implies either in the past or in the present the possession of the
recognised properties of living matter. On the other hand, the expressions
living and lifeless, animate and inanimate, furnish terms which are un-

* La vie et la mort, English translation by W. J. Greenstreet, 1911, p. 54.

7

8 LIFE: ITS NATUKE, OEIGIN AND MAINTENANCE

doubtedly antithetical. Strictly and literally, the words animate and in-
animate express the presence or absence of ' soul ' ; and not in-
frequently we find the terms ' life ' and ' soul ' erroneously employed as if

identical. But it is hardly necessary for me to state that

Life not identical th remar t s j have to make regarding ' life ' must not
with soul.

be taken to apply to the conception to which the word

' soul ' is attached. The fact that the formation of such a conception is
only possible in connection with life, and that the growth and elabora-
tion of the conception has only been possible as the result of the
most complex processes of life in the most complex of living
organisms, has doubtless led to a belief in the identity of life with
soul. But unless the use of the expression ' soul ' is extended to a degree
which would deprive it of all special significance, the distinction between
these terms must be strictly maintained. For the problems of life are

essentially problems of matter ; we cannot conceive of
Problems of life are IT ,1 , , /.

problems of matter. llfe m tne scientmc sense as existing apart from

matter. The phenomena of life are investigated, and
can only be investigated, by the same methods as all other phenomena of
matter, and the general results of such investigations tend to show that
living beings are governed by laws identical with those which govern in-
animate matter. The more we study the manifestations of life the more
we become convinced of the truth of this statement and the less we are
disposed to call in the aid of a special and unknown form of energy to
explain those manifestations.

The most obvious manifestation of life is * spontaneous ' movement.
We see a man, a dog, a bird move, and we know that they are alive. We

place a drop of pond water under the microscope, and

Phenomena indica- see numberless particles rapidly moving within it : we

tive of life. Move- ,..

ment. affirm that it swarms with ' life. We notice a small

mass of clear slirne changing its shape, throwing out
projections of its structureless substance, creeping from one part of the
field of the microscope to another. We recognise that the slime is living ;
we give it a name Amoeba Umax the slug amoeba. We observe similar
movements in individual cells of our own body ; in the white corpuscles of
our blood, in connective tissue cells, in growing nerve cells, in young cells
everywhere. We denote the similarity between these movements and
those of the amoeba by employing the descriptive term ' amoeboid ' for
both. We regard such movements as indicative of the possession of ' life ' ;
nothing seems more justifiable than such an inference.

But physicists * show us movements of a precisely similar character in
substances which no one by any stretch of imagination can regard as
living; movements of oil drops, of organic and inorganic mixtures, even of
mercury globules, which are indistinguishable in their character from
those of the living organisms we have been studying : movements which
* G. Quincke, Annal. d. Physik u. Chem., 1870 and 1888.

LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE 9

can only be described by the same term amoeboid, yet obviously pro-
duced as the result of purely physical and chemical reactions causing

changes in surface tension of the fluids under exami-

Similarity of move- na fcjon.* It is therefore certain that such movements

ments in living and

non-living matter. are not specifically 'vital,' that their presence does

not necessarily denote ' life.' And when we investi-
gate closely even such active movements as those of a vibratile cilium
or a phenomenon so intimately identified with life as the contraction
of a muscle, we find that these present so many analogies with amoeboid
movements as to render it certain that they are fundamentally of the
same character and produced in much the same manner. f Nor can we
for a moment doubt that the complex actions which are characteristic
of the more highly differentiated organisms have been developed in the
course of evolution from the simple movements characterising the activity
of undifferentiated protoplasm ; movements which can themselves, as we
have seen, be perfectly imitated by non-living material. The chain of
evidence regarding this particular manifestation of life movement is
complete. Whether exhibited as the amoeboid movement of the proteus
animalcule or of the white corpuscle of our blood ; as the ciliary motion
of the infusorian or of the ciliated cell ; as the contraction of a muscle
under the governance of the will, or as the throbbing of the human heart
responsive to every emotion of the mind, we cannot but conclude that it
is alike subject to and produced in conformity with the general laws of
matter, by agencies resembling those which cause movements in lifeless
material.]:

It will perhaps be contended that the resemblances between the
movements of living and non-living matter may be only superficial,

and that the conclusion regarding their identity to
Assimilation and , . , , -, . , -,. . -. -, -,

disassimilation. which we are led will be dissipated when we endeavour

to penetrate more deeply into the working of living
substance. For can we not recognise along with the possession of move-
ment the presence of other phenomena which are equally characteristic
of life and with which non-living material is not endowed? Prominent

* The causation not only of movements but of various other manifestations of life
by alterations in surface tension of living substance is ably dealt with by A. B. Macallum
in a recent article in Asher and Spiro's Ergebnisse der Physiologic, 1911. Macallum
has described an accumulation of potassium salts at the more active surfaces of the
protoplasm of many cells, and correlates this with the production of cell-activity
by the effect of such accumulation upon the surface tension. The literature of the
subject will be found in this article.

f G. F. Fitzgerald (Brit. Assoc. Reports, 1898, and Scient. . Trans. Roy. Dublin
Society, 1898) arrived at this conclusion with regard to muscle from purely physical
considerations.

I ' Vital spontaneity, so readily accepted by persons ignorant of biology, is disproved
by the whole history of science. Every vital manifestation is a response to a stimulus,
a provoked phenomenon. It is unnecessary to say this is also the case with brute
bodies, since that is precisely the foundation of the great principle of the inertia of
matter. It is plain that it is also as applicable to living as to inanimate matter. '-
Dastre, op. cit., p. 280.

10 LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE

among the characteristic phenomena of life are the processes of assi-
milation and disassimilation, the taking in of food and its elaboration.*
These, surely, it may be thought, are not shared by matter which is not
endowed with life. Unfortunately for this argument, similar processes
occur characteristically in situations which no one would think of
associating with the presence of life. A striking example of this is
afforded by the osmotic phenomena presented by solutions separated
from one another by semipermeable membranes or films, a condition
which is precisely that which is constantly found in living matter, f

It is not so long ago that the chemistry of organic matter was
thought to be entirely different from that of inorganic substances. But

the line between inorganic and organic chemistry,

Chemical phenomena i , , ,-, -jjiri.il j

accompanying life. which up to the middle 01 the last century appeared

sharp, subsequently became misty and has now dis-
appeared. Similarly the chemistry of living organisms, which is now
a recognised branch of organic chemistry, but used to be considered as
so much outside the domain of the chemist that it could only be dealt
with by those whose special business it was to study ' vital ' processes,
is passing more and more out of the hands of the biologist and into those
of the pure chemist.

Somewhat more than half a century ago Thomas Graham published
his epoch-making observations relating to the properties of matter in

the colloidal state : observations which are proving
The colloid constitu- n j t rn

tion of living matter all-important in assisting our comprehension oi the

identity of physical properties of living substance. For it is becoming

and chemical pro- every day m0 re apparent that the chemistry and
cesses m living and f i n

non-living matter. physics of the living organism are essentially the

chemistry and physics of nitrogenous colloids. Living
substance or protoplasm always, in fact, takes the form of a col-
loidal solution. In this solution the colloids are associated with crystal-
loids (electrolytes), which are either free in the solution or attached
to the molecules of the colloids. Surrounding and enclosing the
living substance thus constituted of both colloid and crystalloid material
is a film, probably also formed of colloid, but which may have a
lipoid substratum associated with it (Overton). This film serves the
purpose of an osmotic membrane, permitting of exchanges by diffusion

* The terms ' assimilation ' and ' disassimilation ' express the physical and chemical
changes which occur within protoplasm as the result of the intake of nutrient material
from the circumambient medium and its ultimate transformation into waste products
which are passed out again into that medium ; the whole cycle of these changes being
embraced under the term 'metabolism.'

f Leduc (The Mechanism of Life, English translation by W. Deane Butcher, 1911)
has given many illustrations of this statement. In the Report of the meeting of 1867
in Dundee is a paper by Dr. J. D. Heaton (On Simulations of Vegetable Growths by
Mineral Substances) dealing with the same class of phenomena. See also J. Hall-
Edwards, Address to Birmingham and Midland Institute, Nov. , 1911. The conditions of
osmosis in cells have been especially studied by Hamburger (Osmotischer Druck und
lonenlehre, Wiesbaden, 1902-4).

LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE 11

between the colloidal solution constituting the protoplasm and the
circumambient medium in which it lives. Other similar films or
membranes occur in the interior of protoplasm. These films have in
many cases specific characters, both physical and chemical, thus favouring
the diffusion of special kinds of material into and out of the protoplasm
and from one part of the protoplasm to another. It is the changes pro-
duced under these physical conditions, associated with those caused by
active chemical agents formed within protoplasm and known as enzymes,
that effect assimilation and disassimilation. Quite similar changes can be
produced outside the body (in vitro) by the employment of methods of
a purely physical and chemical nature. It is true that we are not yet
familiar with all the intermediate stages of transformation of the materials
which are taken in by a living body into the materials which are given out
from it. But since the initial processes and the final results are the same
as they would be on the assumption that the changes are brought about
in conformity with the known laws of chemistry and physics, we may
fairly conclude that all changes in living substance are brought about by
ordinary chemical and physical forces.

Should it be contended that growth and reproduction are properties
possessed only by living bodies and constitute a test by which we may

differentiate between life and non-life, between the

Similarity of the am ' ma t e an d inanimate creation, it must be replied

processes of growth . .

and reproduction in that no contention can be more iallacious. Inorganic

living and non-living crystals grow and multiply and reproduce their like,

given a supply of the requisite pabulum. In most
cases for each kind of crystal there is, as with living organisms, a limit of
growth which is not exceeded, and further increase of the crystalline
matter results not in further increase in size but in multiplication of
similar crystals. Leduc has shown that the growth and division of
artificial colloids of an inorganic nature, when placed in an appropriate
medium, present singular resemblances to the phenomena of the growth
and division of living organisms. Even so complex a process as the
division of a cell-nucleus by karyokinesis as a preliminary to the multi-
plication of the cell by division a phenomenon which would primd facie
have seemed and has been commonly regarded as a distinctive mani-
festation of the life of the cell can be imitated with solutions of a simple
inorganic salt, such as chloride of sodium, containing a suspension of
carbon particles ; which arrange and rearrange themselves under the
influence of the movements of the electrolytes in a manner indistinguish-
able from that adopted by the particles of chromatin in a dividing nucleus.
And in the process of sexual reproduction, the researches of J. Loeb and
others upon the ova of the sea-urchin have proved that we can no longer
consider such an apparently vital phenomenon as the fertilisation of the
egg as being the result of living material brought to it by the sper-
matozoon, since it is possible to start the process of division of the ovum

12 LIFE: ITS NATUEE, OKIGIN AND MAINTENANCE

and the resulting formation of cells, and ultimately of all the tissues and
organs in short, to bring about the development of the whole body if

a simple chemical reagent is substituted for the male

v?tli^m S and vital element in the process of fertilisation. Indeed, even
force. a mechanical or electrical stimulus may suffice to start

development. Kurz und gut, as the Germans say,
vitalism as a working hypothesis has not only had its foundations under-
mined, but most of the superstructure has toppled over, and if any diffi-
culties of explanation still persist, we are justified in assuming that the
cause is to be found in our imperfect knowledge of the constitution and
working of living material. At the best vitalism explains nothing, and
the term ' vital force ' is an expression of ignorance which can bring us
no further along the path of knowledge. Nor is the problem in any
way advanced by substituting for the term 'vitalism' ' neo-vitalism,'
and for ' vital force ' ' biotic energy.' ' New presbyter is but old priest
writ large.'

Further, in its chemical composition we are no longer compelled to
consider living substance as possessing infinite complexity, as was thought
The possibility of the ^ oe the case when chemists first began to break up
synthesis of living the proteins of the body into their simpler con-
stituents. The researches of Miescher, which have
been continued and elaborated by Kossel and his pupils, have acquainted
us with the fact that a body so important for the nutritive and repro-
ductive functions of the cell as the nucleus which may be said indeed to
represent the quintessence of cell-life possesses a chemical constitution
of no very great complexity ; so that we may even hope some day to see
the material which composes it prepared synthetically. And when we
consider that the nucleus is not only itself formed of living substance, but
is capable of causing other living substance to be built up ; is, in fact, the
directing agent in all the principal chemical changes which take place
within the living cell, it must be admitted that we are a long step forward
in our knowledge of the chemical basis of life. That it is the form of
nuclear matter rather than its chemical and molecular structure which is
the important factor in nuclear activity cannot be supposed. The form of
nuclei, as every microscopist knows, varies infinitely, and there are
numerous living organisms in which the nuclear matter is without form,
appearing simply as granules distributed in the protoplasm. Not that the
form assumed and the transformations undergone by the nucleus are with-
out importance ; but it is none the less true that even in an amorphous
condition the material which in the ordinary cell takes the form of a
' nucleus ' may, in simpler organisms which have not in the process of

* B. Moore, in Recent Advances in Physiology, 1906 ; Moore and Roaf, ibid. ; and
Further Advances in Physiology, 1909. Moore lays especial stress on the trans-
formations of energy which occur in protoplasm. See on the question of vitalism
Gley (Revue Scientifique, 1911) and D'Arcy Thompson (Address to Section D at
Portsmouth, 1911).

LIFE: ITS NATURE, OEIGIN AND MAINTENANCE 13

evolution become complete cells, fulfil functions in many respects similar
to those fulfilled by the nucleus of the more differentiated organism.

A similar anticipation regarding the probability of eventual synthetic
production may be made for the proteins of the cell-substance. Con-
siderable progress in this direction has indeed already been made by Emil
Fischer, who has for many years been engaged in the task of building
up the nitrogenous combinations which enter into the formation of the
complex molecule of protein. It is satisfactory to know that the signifi-
cance of the work both of Fischer and of Kossel in this field of biological
chemistry has been recognised by the award to each of these distinguished
chemists of a Nobel prize.

The elements composing living substance are few in number. Those
which are constantly present are carbon, hydrogen, oxygen, and nitrogen.

With these, both in nuclear matter and also, but to a

The chemical con- i egg d e rr ree in the more diffuse living material which

stitution of living

substance. we know as protoplasm, phosphorus is always

associated. ' Ohne Phosphor kein Gedanke ' is an
accepted aphorism ; ' Ohne Phosphor kein Leben ' is equally true.
Moreover, a large proportion, rarely less than 70 per cent., of water
appears essential for any manifestation of life, although not in all cases
necessary for its continuance, since organisms are known which w T ill bear
the loss of the greater part if not the whole of the water they contain
without permanent impairment of their vitality. The presence of
certain inorganic salts is no less essential, chief amongst them being
chloride of sodium and salts of calcium, magnesium, potassium, and iron.
The combination of these elements into a colloidal compound represents
the chemical basis of life ; and when the chemist succeeds in building up
this compound it will without doubt be found to exhibit the phenomena
which we are in the habit of associating with the term ' life.' *

The above considerations seem to point to the conclusion that the
possibility of the production of life i.e., of living material is not so

remote as has been generally assumed. Since the

Source of life. The experiments of Pasteur, few have ventured to affirm
possibility of spon- * . , . . . , , . ,

taneous generation. a belief in the spontaneous generation 01 bacteria and

monads and other micro-organisms, although before his
time this was by many believed to be of universal occurrence. My
esteemed friend Dr. Gharlton Bastian is, so far as I am aware, the only
scientific man of eminence who still adheres to the old creed, and
Dr. Bastian, in spite of numerous experiments and the publication of
many books and papers, has not hitherto succeeded in winning over many
converts to his opinion. I am myself so entirely convinced of the
accuracy of the results which Pasteur obtained are they not within the

* The most recent account of the chemistry of protoplasm is that by Botazzi (Das
Cytoplasma u. die Korpersafte) in Winterstein's Handb. d. vergl. Physiologic, Bd. I.,
1912. The literature is given in this article.

14 LIFE: ITS NATUEE, OKIGIN AND MAINTENANCE

daily and hourly experience of everyone who deals with the sterilisation
of organic solutions ? that I do not hesitate to believe, if living torulae or
mycelia are exhibited to me in flasks which had been subjected to pro-
longed boiling after being hermetically sealed, that there has been some
fallacy either in the premisses or in the carrying out of the operation.
The appearance of organisms in such flasks would not furnish to my
mind proof that they were the result of spontaneous generation.
Assuming no fault in manipulation or fallacy in observation, I should find
it simpler to believe that the germs of such organisms have resisted the
effects of prolonged heat than that they became generated spontaneously.
If spontaneous generation is possible, we cannot expect it to take the
form of living beings which show so marked a degree of differentiation,
both structural and functional, as the organisms which are described
as making their appearance in these experimental flasks.* Nor should
we expect the spontaneous generation of living substance of any kind to
occur in a fluid the organic constituents of which have been so altered by
heat that they can retain no sort of chemical resemblance to the organic
constituents of living matter. If the formation of life of living
substance is possible at the present day and for my own part I
see no reason to doubt it a boiled infusion of organic matter and still
less of inorganic matter is the last place in which to look for it. Our
mistrust of such evidence as has yet been brought forward need not,
however, preclude us from admitting the possibility of the formation of
living from non-living substance.!

Setting aside, as devoid of scientific foundation, the idea of immediate
supernatural intervention in the first production of life, we are not only

justified in believing, but compelled to believe, that

Life a product living matter must have owed its origin to causes

of evolution. ..,.', .

similar in character to those which have been instru-
mental in producing all other forms of matter in the universe ; in other

* It is fair to point out that Dr. Bastian suggests that the formation of ultra-
microscopic living particles may precede the appearance of the microscopic organisms
which he describes. The Origin of Life, 1911, p. 65.

f The present position of the subject is succinctly stated by Dr. Chalmers Mitchell
in his article on ' Abiogenesis ' in the Encyclopedia Britannica. Dr. Mitchell adds :
' It may be that in the progress of science it may yet be possible to construct living
protoplasm from non-living material. The refutation of abiogenesis has no further
bearing on this possibility than to make it probable that if protoplasm ultimately be
formed in the laboratory, it will be by a series of steps, the earlier steps being the forma-
tion of some substance, or substances, now unknown, which are not protoplasm. Such
intermediate stages may have existed in the past.' And Huxley in his Presidential
Address at Liverpool in 1870 says : ' But though I cannot express this conviction '
(i.e., of the impossibility of the occurrence of abiogenesis, as exemplified by the
appearance of organisms in hermetically sealed and sterilised flasks) ' too strongly,
I must carefully guard myself against the supposition that I intend to suggest that no
such thing as abiogenesis ever has taken place in the past or ever will take place in the
future. With organic chemistry, molecular physics, and physiology yet in their
infancy and every day making prodigious strides, I think it would be the height of
presumption for any man to say that the conditions under which matter assumes the
properties we call "vital" may not, some day, be artificially brought together.'

LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE 15

words, to a process of gradual evolution.* But it has been customary of
late amongst biologists to shelve the investigation of the mode of origin
of life by evolution from non-living matter by relegating its solution to
some former condition of the earth's history, when, it is assumed, oppor-
tunities were accidentally favourable for the passage of inanimate matter
into animate ; such opportunities, it is also assumed, having never since
recurred and being never likely to recur, f

Various eminent scientific men have even supposed that life has not
actually originated upon our globe, but has been brought to it from
another planet or from another stellar system. Some of my audience
may still remember the controversy that was excited when the theory of
the origin of terrestrial life by the intermediation of a meteorite was
propounded by Sir William Thomson in his Presidential Address at the
meeting of this Association in Edinburgh in 1871. To this ' meteorite '
theory J the apparently fatal objection was raised that it would take
some sixty million years for a meteorite to travel from the nearest stellar
system to our earth, and it is inconceivable that any kind of life could
be maintained during such a period. Even from the nearest planet
150 years would be necessary, and the heating of the meteorite in
passing through our atmosphere and at its impact with the earth would,
in all probability, destroy any life which might have existed within it.
A cognate theory, that of cosmic panspermia, assumes that life may exist
and may have existed indefinitely in cosmic dust in the interstellar spaces
(Bichter, 1865 ; Cohn, 1872), and may with this dust fall slowly to the
earth without undergoing the heating which is experienced by a meteorite.
Arrhenius, who adopts this theory, states that if living germs were
carried through the ether by luminous and other radiations the time
necessary for their transportation from our globe to the nearest stellar
system would be only nine thousand years, and to Mars only twenty
days !

But the acceptance of such theories of the arrival of life on the earth
does not bring us any nearer to a conception of its actual mode of origin ;
on the contrary it merely serves to banish the investigation of the question
to some conveniently inaccessible corner of the universe and leaves us in
the unsatisfactory position of affirming not only that we have no know-

* The arguments in favour of this proposition have been arrayed by Meldola in his
Herbert Spencer Lecture, 1910, pp. 16-24. Meldola leaves the question open whether
such evolution has occurred only in past years or is also taking place now. He con-
cludes that whereas -certain carbon compounds have survived by reason of possessing
extreme stability, others the precursors of living matter survived owing to the
possession of extreme lability and adaptability to variable conditions of environment.
A similar suggestion was previously made by Lockyer, Inorganic Evolution, 1900,
pp. 169, 170.

f T. H. Huxley, Presidential Address, 1870 ; A. B. Macallum, ' On the Origin of
Life on the Globe,' in Trans. Canadian Institute, VIII.

| First suggested, according to Dastre, by de Salles-Guyon (Dastre, op. cit., p. 252).
The theory received the support of Helmholtz.

Worlds in the Making, transl. by H. Borns, chap, viii., p. 221, 1908.

16 LIFE: ITS NATUEE, OKIGIN AND MAINTENANCE

ledge as to the mode of origin of life which is unfortunately true but
that we never can acquire such knowledge which it is to be hoped is not
true.* Knowing what we know, and believing what we believe, as to the
part played by evolution in the development of terrestrial matter, we are,
I think (without denying the possibility of the existence of life in other
parts of the universe t), justified in regarding these cosmic theories as
inherently improbable at least in comparison with the solution of the
problem which the evolutionary hypothesis offers. J

I assume that the majority of my audience have at least a general
idea of the scope of this hypothesis, the general acceptance of which has

within the last sixty years altered the whole aspect

The evolutionary hy- not only of biology, but of every other branch of

pothesis as applied J . . J

to the origin of life, natural science, including astronomy, geology, physics,

and chemistry. To those who have not this know-
ledge I would recommend the perusal of a little book by Professor
Judd, entitled ' The Coming of Evolution,' which has recently appeared
as one of the Cambridge manuals. I know of no similar book in
which the subject is as clearly and succinctly treated. Although the
author nowhere expresses the opinion that the actual origin of life
on the earth has arisen by evolution from non-living matter, it is
impossible to read either this or any similar exposition in which
the essential unity of the evolutionary process is insisted upon
without concluding that the origin of life must have been due to the
same process, this process being, without exception, continuous, and
admitting of no gap at any part of its course. Looking therefore at the
evolution of living matter by the light which is shed upon it from the
study of the evolution of matter in general, we are led to regard it as
having been produced, not by a sudden alteration, whether exerted by
natural or supernatural agency, but by a gradual process of change from
material which was lifeless, through material on the borderland between

* ' The history of science shows how dangerous it is to brush aside mysteries
i.e., unsolved problems and to interpose the barrier placarded " eternal no thorough-
fare." ' R. Meldola, Herbert Spencer Lecture, 1910.

t Some authorities, such as Errera, contend, with much probability, that the
conditions in interstellar space are such that life, as we understand it, could not
possibly exist there.

J As Verworn points out, such theories would equally apply to the origin of any
other chemical combination, whether inorganic or organic, which is met with on our
globe, so that they lead directly to absurd conclusions. Allgemcine Physiologic, 1911.

As Meldola insists, this general acceptance was in the first instance largely due
to the writings of Herbert Spencer : ' We are now prepared for evolution in every
domain. ... As in the case of most great generalisations, thought had been moving
in this direction for many years. . . . Lamarck and Buffon had suggested a definite
mechanism of organic development, Kant and Laplace a principle of celestial evolu-
tion, while Lyell had placed geology upon an evolutionary basis. The principle of
continuity was beginning to be recognised in physical science. ... It was Spencer
who brought these independent lines of thought to a focus, and who was the first to
make any systematic attempt to show that the law of development expressed in its
widest and most abstract form was universally followed throughout cosmical processes,
inorganic, organic, and super-organic.' Op. cit., p. 14.

LIFE: ITS NATUKE, OEIGIN AND MAINTENANCE 17

inanimate and animate, to material which has all the characteristics to
which we attach the term ' life.' So far from expecting a sudden leap
from an inorganic, or at least an unorganised, into an organic and
organised condition, from an entirely inanimate substance to a completely
animate state of being, should we not rather expect a gradual procession
of changes from inorganic to organic matter, through stages of gradually
increasing complexity until material which can be termed living is
attained ? And in place of looking for the production of fully formed
living organisms in hermetically sealed flasks, should we not rather search
Nature herself, under natural conditions, for evidence of the existence,
either in the past or in the present, of transitional forms between living
and non-living matter?

The difficulty, nay the impossibility, of obtaining evidence of such
evolution from the past history of the globe is obvious. Both the hypo-
thetical transitional material and the living material which was originally
evolved from it may, as Macallum has suggested, have taken the form of
diffused ultra-microscopic particles of living substance * ; and even if they
were not diffused but aggregated into masses, these masses could have
been physically nothing more than colloidal watery slime which would
leave no impress upon any geological formation. Myriads of years may
have elapsed before some sort of skeleton in the shape of calcareous or
siliceous spicules began to evolve itself, and thus enabled ' life,' which
must already have possessed a prolonged existence, to make any sort of
geological record. It follows that in attempting to pursue the evolution
of living matter to its beginning in terrestrial history we can only expect to
be confronted with a blank wall of nescience.

The problem would appear to be hopeless of ultimate solution, if
we are rigidly confined to the supposition that the evolution of life has
only occurred once in the past history of the globe. But are we justified
in assuming that at one period only, and as it were by a fortunate and
fortuitous concomitation of substance and circumstance, living matter
became evolved out of non-living matter life became established? Is
there any valid reason to conclude that at some previous period of its
history our earth was more favourably circumstanced for the production of
life than it is now ? f I have vainly sought for such reason, and if none
be forthcoming the conclusion forces itself upon us that the evolution
of non-living into living substance has happened more than once and we
can be by no means sure that it may not be happening still.

* There still exist in fact forms of life which the microscope cannot show us (E. A.
Minchin, Presidential Address to Quekett Club, 1911), and germs which are capable of
passing through the pores of a Chamberland filter.

f Chalmers Mitchell (Art. Life,' Encycl. Brit., eleventh edition) writes as
follows : ' It has been suggested from time to time that conditions very unlike those
now existing were necessary for the first appearance of life, and must be repeated if
living matter is to be reconstituted artificially. No support for such a view can be
derived from observations of the existing conditions of life.' Cf. also J. Hall-Edwards,
op. cit.

18 LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE

It is true that up to the present there is no evidence of such hap-
pening : no process of transition has hitherto been observed. But on the
other hand, is it not equally true that the kind of evidence which would
be of any real value in determining this question has not hitherto been
looked for ? We may be certain that if life is being produced from non-
living substance it will be life of a far simpler character than any that
has yet been observed in material which we shall be uncertain whether
to call animate or inanimate, even if we are able to detect it at all,
and which we may not be able to visualise physically even after we
have become convinced of its existence.* But we can look with the
mind's eye and follow in imagination the transformation which non-
living matter may have undergone and may still be undergoing to pro-
duce living substance. No principle of evolution is better founded than
that insisted upon by Sir Charles Lyell, justly termed by Huxley ' the
greatest geologist of his time,' that we must interpret the past history
of our globe by the present ; that we must seek for an explanation of
what has happened by the study of what is happening ; that, given
similar circumstances, what has occurred at one time will probably occur
at another. The process of evolution is universal. The inorganic
materials of the globe are continually undergoing transition. New
chemical combinations are constantly being formed and old ones broken
up ; new elements are making their appearance and old elements dis-
appearing.! Well may we ask ourselves why the production of living
matter alone should be subject to other laws than those which have
produced, and are producing, the various forms of non-living matter ;
why what has happened may not happen. If living matter has been
evolved from lifeless in the past, we are justified in accepting the
conclusion that its evolution is possible in the present and in the future.
Indeed, we are not only justified in accepting this conclusion, we are
forced to accept it. When or where such change from non-living to
living matter may first have occurred, when or where it may have
continued, when or where it may still be occurring, are problems as
difficult as they are interesting, but we have no right to assume that
they are insoluble.

Since living matter always contains water as its most abundant
constituent, and since the first living organisms recognisable as such
in the geological series were aquatic, it has generally been assumed that
life must first have made its appearance in the depths of the ocean.]:

* ' Spontaneous generation of life could only be perceptually demonstrated by filling
in the long terms of a series between the complex forms of inorganic and the simplest
forms of organic substance. Were this done, it is quite possible that we should be
unable to say (especially considering the vagueness of our definitions of life) where life
began or ended.' K. Pearson, Grammar of Science, second edition, 1900, p. 350.

f See on the production of elements, W. Crookes, Address to Section B, Brit.
Assoc., 1886 ; T. Preston, Nature, vol. lx., p. 180; J. J. Thomson, Phil. Mag., 1897,
p. 311 ; Norman Lockyer, op. cit., 1900 ; G. Darwin, Pres. Addr. Brit. Assoc., 1905.

I For arguments in favour of the first appearance of life having been in the sea,

LIFE: ITS NATURE, ORIGIN AND MAINTENANCE 19

Is it, however, certain that the assumption that life originated in the sea
is correct ? Is not the land-surface of our globe quite as likely to have
been the nidus for the evolutionary transformation of non-living into
living material as the waters which surround it ? Within this soil almost
any chemical transformation may occur ; it is subjected much more
than matters dissolved in sea-water to those fluctuations of moisture,
temperature, electricity, and luminosity which are potent in producing
chemical changes. But whether life, in the form of a simple slimy
colloid, originated in the depths of the sea or on the surface of the land,
it would be equally impossible for the geologist to trace its beginnings,
and were it still becoming evolved in the same situations, it would be
almost as impossible for the microscopist to follow its evolution. We
are therefore not likely to obtain direct evidence regarding such a
transformation of non-living into living matter in Nature, even if it is
occurring under our eyes.

An obvious objection to the idea that the production of living matter
from non-living has happened more than once is that, had this been the
case, the geological record should reveal more than one palaeontological
series. This objection assumes that evolution would in every case take
an exactly similar course and proceed to the same goal an assumption
which is, to say the least, improbable. If, as might well be the case,
in any other palaeontological series than the one with which we are
acquainted the process of evolution of living beings did not proceed
beyond Protista, there would be no obvious geological evidence regarding
it; such evidence would only be discoverable by a carefully directed
search made with that particular object in view.* I would not by any
means minimise the difficulties which attend the suggestion that the
evolution of life may have occurred more than once or may still be
happening, but on the other hand, it must not be ignored that those
which attend the assumption that the production of life has occurred
once only are equally serious. Indeed, had the idea of the possibility
of a multiple evolution of living substance been first in the field, I
doubt if the prevalent belief regarding a single fortuitous production
of life upon the globe would have become established among biologists-
so much are we liable to be influenced by the impressions we receive in
scientific childhood !

see A. B. Macallum, ' The Palseochemistry of the Ocean,' Trans. Canad. Instit.,
1903-4.

* Lankester (Art. 'Protozoa,' Encycl. Brit., tenth edition) conceives that the first
protoplasm fed on the antecedent steps in its own evolution. F. J. Allen (Brit. Assoc.
Reports, 1896) comes to the conclusion that living substance is probably constantly
being produced, but that this fails to make itself evident owing to the substance being
seized and assimilated by existing organisms. He believes that ' in accounting for the
first origin of life on this earth it is not necessary that, as Pfluger assumed, the planet
should have been at a former period a glowing fire-ball.' He 'prefers to believe that
the circumstances which support life would also favour its origin.' And elsewhere :
' Life is not an extraordinary phenomenon, not even an importation from some other
sphere, but rather the actual outcome of circumstances on this earth.'

20 LIFE: ITS NATURE, ORIGIN AND MAINTENANCE

Assuming the evolution of living matter to have occurred whether
once only or more frequently matters not for the moment and in the

form suggested, viz., as a mass of colloidal slime

Further course of possessing the property of assimilation and therefore
evolution of life. j j.- urn t

of growth, reproduction would lollow as a matter or

course. For all material of this physical nature fluid or semi-fluid in
character has a tendency to undergo subdivision when its bulk exceeds a
certain size. The subdivision may be into equal or nearly equal parts, or
it may take the form of buds. In either case every separated part would
resemble the parent in chemical and physical properties, and would
equally possess the property of taking in and assimilating suitable
material from its liquid environment, growing in bulk and reproducing
its like by subdivision. Omne vivum e vivo. In this way from any
beginning of living material a primitive form of life would spread, and
would gradually people the globe. The establishment of life being once
effected, all forms of organisation follow under the inevitable laws of
evolution. Ce nest que le premier pas qui coute I

We can trace in imagination the segregation of a more highly
phosphorised portion of the primitive living matter, which we may now
consider to have become more akin to the protoplasm of organisms
with which we are familiar. This more phosphorised portion might
not for myriads of generations take the form of a definite nucleus, but
it would be composed of material having a composition and qualities
similar to those of the nucleus of a cell. Prominent among these
qualities is that of catalysis the function of effecting profound
chemical changes in other material in contact with it without itself
undergoing permanent change. This catalytic function may have been
exercised directly by the living substance or may have been carried
on through the agency of the enzymes already mentioned, which are also
of a colloid nature but of simpler constitution than itself, and which
differ from the catalytic agents employed by the chemist in the fact that
they produce their effects at a relatively low temperature. In the course
of evolution special enzymes would become developed for adaptation to
special conditions of life, and with the appearance of these and other
modifications, a process of differentiation of primitive living matter into
individuals with definite specific characters gradually became established.
We can conceive of the production in this way from originally undifferen-
tiated living substance of simple differentiated organisms comparable to
the lowest forms of Protista. But how long it may have taken to arrive
at this stage we have no means of ascertaining. To judge from the evi-
dence afforded by the evolution of higher organisms it would seem that a
vast period of time would be necessary for even this amount of organisation
to establish itself.

The next important phase in the process of evolution would be the
segregation and moulding of the diffused or irregularly aggregated nuclear

LIFE: ITS NATURE, ORIGIN AND MAINTENANCE 21

matter into a definite nucleus around which all the chemical activity
of the organism will in future be centred. Whether this change were

due to a slow and gradual process of segregation or

of the nature of a J um P' such as Nature does occa-
sionally make, the result would be the advancement of

the living organism to the condition of a complete nucleated cell : a
material advance not only in organisation but still more important in
potentiality for future development. Life is now embodied in the cell, and
every living being evolved from this will itself be either a cell or a cell-
aggregate. Oinnis cellula e celluld.

After the appearance of a nucleus but how long after it is impossible
to conjecture another phenomenon appeared upon the scene in the occa-
sional exchange of nuclear substance between cells.

se^Sfferences. In this manner became established the process of

sexual reproduction. Such exchange in the unicellular
organism might and may occur between any two cells forming the species,
but in the multicellular organism it became like other f unctions -
specialised in particular cells. The result of the exchange is rejuvene-
scence ; associated with an increased tendency to subdivide and to pro-
duce new individuals. This is due to the introduction of a stimulating or
catalytic chemical agent into the cell which is to be rejuvenated, as is
proved by the experiments of 'Loeb already alluded to. It is true that the
chemical material introduced into the germ-cell in the ordinary process of
its fertilisation by the sperm-cell is usually accompanied by the introduc-
tion of definite morphological elements which blend with others already
contained within the germ-cell, and it is believed that the transmission of
such morphological elements of the parental nuclei is related to the trans-
mission of parental qualities. But we must not be blind to the possibility
that those transmitted qualities may be connected with specific chemical
characters of the transmitted elements ; in other words, that heredity also
is one of the questions the eventual solution of which we must look to the
chemist to provide.

So far we have been chiefly considering life as it is found in the
simplest formsof living substance, organisms for the most part entirely micro-
scopic and neither distinctively animal nor vegetable,
Aggregate life. which have sometimes been grouped together as a sepa-

rate kingdom of animated nature that of Protista. But
persons unfamiliar with the microscope are not in the habit of associating
the term ' life ' with microscopic organisms, whether these take the form
of cells or of minute portions of living substance which have not yet
attained to that dignity. We most of us speak and think of life as it
occurs in ourselves and other animals with which we are familiar ; and as
we find it in the plants around us. We recognise it in these by the
possession of certain properties movement, nutrition, growth, and repro-
duction. We are not aware by intuition, nor can we ascertain without the

22 LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE

employment of the microscope, that we and all the higher living beings,
whether animal or vegetable, are entirely formed of aggregates of nucleated
cells, each microscopic and each possessing its own life. Nor could we
suspect by intuition that what we term our life is not a single indivisible
property, capable of being blown out with a puff like the flame of a candle ;
but is the aggregate of the lives of many millions of living cells of which
the body is composed. It is but a short while ago that this cell constitu-
tion was discovered : it occurred within the lifetime, even within the
memory, of some who are still with us. What a marvellous distance we
have travelled since then in the path of knowledge of living organisms !
The strides which were made in the advance of the mechanical sciences
during the nineteenth century, which is generally considered to mark that
century as an age of unexampled progress, are as nothing in comparison
with those made in the domain of biology, and their interest is entirely
dwarfed by that which is aroused by the facts relating to the phenomena
of life which have accumulated within the same period. And not the least
remarkable of these facts is the discovery of the cell-structure of plants
and animals.

Let us consider how cell-aggregates came to be evolved from organisms
consisting of single cells. Two methods are possible viz. : (1) The

adhesion of a number of originally separate indi-
viduals ; ( 2 ) the subdivision of a single individual
without the products of its subdivision breaking loose
from one another. No doubt this last is the manner whereby the
cell-aggregate was originally formed, since it is that by which it is still
produced, and we know that the life-history of the individual is an
epitome of that of the species. Such aggregates were in the beginning
solid ; the cells in contact with one another and even in continuity : sub-
sequently a space or cavity became formed in the interior of the mass,
which was thus converted into a hollow sphere. All the cells of the aggre-
gate were at first perfectly similar in structure and in function ; there was
no subdivision of labour. All would take part in effecting locomotion ; all
would receive stimuli from outside ; all would take in and digest nutrient
matter, which would then be passed into the cavity of the sphere to serve
as a common store of nourishment. Such organisms are still found, and
constitute the lowest types of Metazoa. Later one part of the hollow
sphere became dimpled to form a cup ; the cavity of the sphere became cor-
respondingly altered in shape. With this change in structure differentia-
tion of function between the cells covering the outside and those lining the
inside of the cup made its appearance. Those on the outside subserved
locomotor functions and received and transmitted from cell to cell stimuli,
physical or chemical, received by the organism ; while those on the inside,
being freed from such functions, tended to specialise in the direction of
the inception and digestion of nutrient material; which, passing from
them into the cavity of the invaginated sphere, served for the nourish-

LIFE: ITS NATUKE, OKIGIN AND MAINTENANCE 23

ment of all the cells composing the organism. The further course of
evolution produced many changes of form and ever-increasing complexity
of the cavity thus produced by simple invagination. Some of the cell-
aggregates settled down to a sedentary life, becoming plant-like in appear-
ance and to some extent in habit. Such organisms, complex in form but
simple in structure, are the Sponges. Their several parts are not, as in
the higher Metazoa, closely interdependent : the destruction of any one part,
however extensive, does not either immediately or ultimately involve
death of the rest: all parts function separately, although doubtless
mutually benefiting by their conjunction, if only by slow diffusion of
nutrient fluid throughout the mass. There is already some differentiation
in these organisms, but the absence of a nervous system prevents any
general co-ordination, and the individual cells are largely independent of
one another.

Our own life, like that of all the higher animals, is an aggregate life ;
the life of the whole is the life of the individual cells. The life of some
of these cells can be put an end to, the rest may continue to live. This
is, in fact, happening every moment of our lives. The cells which cover
the surface of our body, which form the scarf-skin and the hair and nails,
are constantly dying, and the dead cells are rubbed off or cut away, their
place being taken by others supplied from living layers beneath. But the
death of these cells does not affect the vitality of the body as a whole.
They serve merely as a protection or an ornamental covering, but are
otherwise not material to our existence. On the other hand, if a few cells,
such as those nerve-cells under the influence of which respiration is
carried on, are destroyed or injured, within a minute or two the whole
living machine comes to a standstill, so that to the bystander the patient is
dead ; even the doctor will pronounce life to be extinct. But this pro-
nouncement is correct only in a special sense. What has happened is
that, owing to the cessation of respiration, the supply of oxygen to the
tissues is cut off. And since the manifestations of life cease without this
supply, the animal or patient appears to be dead. If, however, within a
short period we supply the needed oxygen to the tissues requiring it, all
the manifestations of life reappear.

It is only some cells which lose their vitality at the moment of
so-called ' general death.' Many cells of the body retain their individual
life under suitable circumstances long after the rest of the body is dead.
Notable among these are muscle-cells. Me William showed that the
muscle-cells of the blood-vessels give indications of life several days after
an animal has been killed. The muscle-cells of the heart in mammals
have been revived and caused to beat regularly and strongly many hours
after apparent death. In man this result has been obtained as many as
eighteen hours after life has been pronounced extinct (Kuliabko) ; in
animals after days have elapsed. Waller has shown that indications of life
can be elicited from various tissues many hours and even days after

24 LIFE: ITS NATURE, OKIGIN AND MAINTENANCE

general death. Sherrington observed the white corpuscles of the blood
to be active when kept in a suitable nutrient fluid weeks after removal
from the blood-vessels. A French histologist, Jolly, has found that the
white corpuscles of the frog, if kept in a cool place and under suitable
conditions, show at the end of a year all the ordinary manifestations of
life. Carrell and Burrows have observed activity and growth to continue
for long periods in the isolated cells of a number of tissues and organs kept
under observation in a suitable medium. Carrell has succeeded in
substituting entire organs obtained after death from one animal for those
of another of the same species, and has thereby opened up a field of
surgical treatment, the limits of which cannot yet be descried. It is a well-
established fact that any part of the body can be maintained alive for hours
isolated from the rest if perfused with serum (Kronecker, frog-heart), or
with an oxygenated solution of salts in certain proportions (Ringer). Such
revival and prolongation of the life of separated organs is an ordinary pro-
cedure in laboratories of physiology. Like all the other instances enume-
rated, it is based on the fact that the individual cells of an organ have a
life of their own which is largely independent, so that they will continue in
suitable circumstances to live, although the rest of the body to which they
belonged may be dead.

But some cells, and the organs which are formed of them, are more
necessary to maintain the life of the aggregate than others, on account of
the nature of the functions which have become specialised in them. This
is the case with the nerve-cells of the respiratory centre, since they
preside over the movements which are necessary to effect oxygenation of
the blood. It is also true for the cells which compose the heart, since
this serves to pump oxygenated blood to all other cells of the body : with-
out such blood most cells soon cease to live. Hence we examine
respiration and heart to determine if life is present : when one or both of
these are at a standstill we know that life cannot be maintained. These
are not the only organs necessary for the maintenance of life, but the loss
of others can be borne longer, since the functions which they subserve,
although useful or even essential to the organism, can be dispensed with
for a time. The life of some cells is therefore more, of others less
necessary for maintaining the life of the rest. On the other hand, the
cells composing certain organs have in the course of evolution ceased to
be necessary, and their continued existence may even be harmful.
Wiedersheim has enumerated more than a hundred of these organs in the
human body. Doubtless Nature is doing her best to get rid of them for
us, and our descendants will some day have ceased to possess a vermiform
appendix or a pharyngeal tonsil : until that epoch arrives we must rely
for their removal on the more rapid methods of surgery !

We have seen that in the simplest multicellular organisms, where one
cell of the aggregate differs but little from another, the conditions for the
maintenance of the life of the whole are nearly as simple as those for

LIFE: ITS NATURE, ORIGIN AND MAINTENANCE 25

individual cells. But the life of a cell-aggregate such as composes the
bodies of the higher animals is maintained not only by the conditions

for the maintenance of the life of the individual cell

The maintenance of bei k t f avou rable, but also by the co-ordination of

the life of the cell- ,

aggregate in the the varied activities of the cells which form the aggre-

higher animals. g a t e . Whereas in the lowest Metazoa all cells of the

mechanisms. aggregate are alike in structure and function and perform

and share everything in common, in higher animals
(and for that matter in the higher plants also) the cells have become special-
ised, and each is only adapted for the performance of a particular function.
Thus the cells of the gastric glands are only adapted for the secretion of
gastric juice, the cells of the villi for the absorption of digested matters
from the intestine, the cells of the kidney for the removal of waste products
and superfluous water from the blood, those of the heart for pumping
blood through the vessels. Each of these cells has its individual life and
performs its individual functions. But unless there were some sort of
co-operation and subordination to the needs of the body generally, there
would be sometimes too little, sometimes too much gastric juice secreted ;
sometimes too tardy, sometimes too rapid an absorption from the intes-
tine ; sometimes too little, sometimes too much blood pumped into the
arteries, and so on. As the result of such lack of co-operation the life of
the whole would cease to be normal and would eventually cease to be
maintained.

We have already seen what are the conditions which are favourable
for the maintenance of life of the individual cell, no matter where situated.
The principal condition is that it must be bathed by a nutrient fluid of
suitable and constant composition. In higher animals this fluid is the
lymph, which bathes the tissue elements and is itself constantly supplied
with fresh nutriment and oxygen by the blood. Some tissue-cells are
directly bathed by blood ; and in invertebrates, in which there is no special
system of lymph-vessels, all the tissues are thus nourished. All cells both
take from and give to the blood, but not the same materials or to an equal
extent. Some, such as the absorbing cells of the villi, almost exclusively
give ; others, such as the cells of the renal tubules, almost exclusively take.
Nevertheless, the resultant of all the give and take throughout the body
serves to maintain the composition of the blood constant under all circum-
stances. In this way the first condition of the maintenance of the life of
the aggregate is fulfilled by insuring that the life of the individual cells
composing it is kept normal.

The second essential condition for the maintenance of life of the cell-
aggregate is the co-ordination of its parts and the due regulation of their
activity, so that they may work together for the benefit of the whole.
In the animal body this is effected in two ways : first, through
the nervous system ; and second, by the action of specific chemical sub-
stances which are formed in certain organs and carried by the blood to

26 LIFE: ITS NATUBE, OEIGIN AND MAINTENANCE

other parts of the body, the cells of which they excite to activity. These
substances have received the general designation of ' hormones ' (op/zaw, to
stir up), a term introduced by Professor Starling. Their action, and indeed
their very existence, has only been recognised of late years, although the
part which they play in the physiology of animals appears to be only
second in importance to that of the nervous system itself ; indeed, main-
tenance of life may become impossible in the absence of certain of these
hormones.

Before we consider the manner in which the nervous system serves to
Part played by the co-ordinate the life of the cell-aggregate, let us see how
nervous system in it has become evolved.

f S lr?geluT Ce f The first 8te P in the P rocess was taken when

Evolution of a ner- certain of the cells of the external layer became

vous system. specially sensitive to stimuli from outside, whether

caused by mechanical impressions (tactile and auditory stimuli) or
impressions of light and darkness (visual stimuli) or chemical impres-
sions. The effects of such impressions were probably at first simply
communicated to adjacent cells and spread from cell to cell throughout the
mass. An advance was made when the more impressionable cells threw
out branching feelers amongst the other cells of the organism. Such
feelers would convey the effects of stimuli with greater rapidity and
directness to distant parts. They may at first have been retractile, in this
respect resembling the long pseudopodia of certain Ehizopoda. When they
became fixed they would be potential nerve-fibres and would represent the
beginning of a nervous system. Even yet (as Eoss Harrison has shown),
in the course of development of nerve-fibres, each fibre makes its appear-
ance as an amoeboid cell-process which is at first retractile, but gradually
grows into the position it is eventually to occupy and in which it will become
fixed.

In the further course of evolution a certain number of these specialised
cells of the external layer sank below the general surface, partly perhaps
for protection, partly for better nutrition : they became nerve-cells. They
remained connected with the surface by a prolongation which became an
afferent or sensory nerve-fibre, and through its termination between the
cells of the general surface continued to receive the effects of external
impressions ; on the other hand, they continued to transmit these impres-
sions to other, more distant cells by their efferent prolongations. In the
further course of evolution the nervous system thus laid down became
differentiated into distinct afferent, efferent, and intermediary portions.
Once established, such a nervous system, however simple, must dominate
the organism, since it would furnish a mechanism whereby the individual
cells would work together more effectually for the mutual benefit of the
whole.

It is the development of the nervous system, although not proceeding
in all classes along exactly the same line, which is the most prominent

LIFE: ITS NATURE, ORIGIN AND MAINTENANCE 27

feature of the evolution of the Metazoa. By and through it all impressions
reaching the organism from the outside are translated into contraction or
some other form of cell-activity. Its formation has been the means of
causing the complete divergence of the world of animals from the world of
plants, none of which possess any trace of a nervous system. Plants react,
it is true, to external impressions, and these impressions produce profound
changes and even comparatively rapid and energetic movements in parts
distant from the point of application of the stimulus as in the well-known
instance of the sensitive plant. But the impressions are in all cases propa-
gated directly from cell to cell not through the agency of nerve-fibres; and in
the absence of anything corresponding to a nervous system it is not possible
to suppose that any plant can ever acquire the least glimmer of intelligence.
In animals, on the other hand, from a slight original modification of cer-
tain cells has directly proceeded in the course of evolution the elaborate
structure of the nervous system with ail its varied and complex functions,
which reach their culmination in the workings of the human intellect.
' What a piece of work is a man ! How noble in reason ! How infinite in
faculty ! In form and moving how express and admirable ! In action
how like an angel ! In apprehension how like a god ! ' But lest he be
elated with his psychical achievements, let him remember that they are but
the result of the acquisition by a few cells in a remote ancestor of a slightly
greater tendency to react to an external stimulus, so that these cells were
brought into closer touch with the outer world ; while on the other hand,
by extending beyond the circumscribed area to which their neighbours
remained restricted, they gradually acquired a dominating influence over
the rest. These dominating cells became nerve-cells ; and now not
only furnish the means for transmission of impressions from one part of
the organism to another, but in the progress of time have become the
seat of perception and conscious sensation, of the formation and
association of ideas, of memory, of volition, and all the manifestations of
the mind.

The most conspicuous part played by the nervous system in the pheno-
mena of life is that which produces and regulates the general movements

of the body movements brought about by the so-called
voluntary muscles. These movements are actually the
system. Voluntary result of impressions imparted to sensory or afferent
movements. nerves at the periphery e.g., in the skin or in the

several organs of special sense ; the effect of these impressions may not be
immediate, but can be stored for an indefinite time in certain cells of the
nervous system. The regulation of movements whether they occur
instantly after reception of the peripheral impression or result after a cer-
tain lapse of time ; whether they are accompanied by conscious sensation
or are of a purely reflex and unconscious character is an intricate process,
and the conditions of their co-ordination are of a complex nature involving
not merely the causation and contraction of certain muscles, but also the

28 LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE

prevention of the contraction of others. For our present knowledge of
these conditions we are largely indebted to the researches of Professor
Sherrington.

A less conspicuous but no less important part played by the nervous
system is that by which the contractions of involuntary muscles are

regulated. Under normal circumstances these are
always independent of consciousness, but their regula-
tion is brought about in much the same way as is that
of the contractions of voluntary muscles viz., as the result of impressions
received at the periphery. These are transmitted by afferent fibres to
the central nervous system, and from the latter other impulses are sent
down, mostly along the nerves of the sympathetic or autonomic system
of nerves, which either stimulate or prevent contraction of the involun-
tary muscles. Many involuntary muscles have a natural tendency to
continuous or rhythmic contraction which is quite independent of the
central nervous system ; in this case the effect of impulses received from
the latter is merely to increase or diminish the amount of such contrac-
tion. An example of this double effect is observed in connection with

the heart, which although it can contract regularly
Effects of emotions. -, * n re F n

and rhythmically when cut on trom the nervous

system and even if removed from the body is normally stimulated to
increased activity by impulses coming from the central nervous system
through the sympathetic, or to diminished activity by others coming
through the vagus. It is due to the readiness by which the action
of the heart is influenced in these opposite ways by the spread of
impulses generated during the nerve-storms which we term ' emotions '
that in the language of poetry, and even of every day, the word ' heart '
has become synonymous with the emotions themselves.

The involuntary muscle of the arteries has its action similarly balanced.
When its contraction is increased, the size of the vessels is lessened and
they deliver less blood ; the parts they supply accordingly become pale in
colour. On the other hand, when the contraction is diminished the
vessels enlarge and deliver more blood ; the parts which they supply
become correspondingly ruddy. These changes in the arteries, like the
effects upon the heart, may also be produced under the influence of
emotions. Thus ' blushing ' is a purely physiological phenomenon due to
diminished action of the muscular tissue of the arteries, whilst the pallor
produced by fright is caused by an increased contraction of that tissue.
Apart, however, from these conspicuous effects, there is constantly pro-
ceeding a less apparent but not less important balancing action between
the two sets of nerve-fibres distributed to heart and blood-vessels ; which
are influenced in one direction or another by every sensation which we
experience and even by impressions of which we may be wholly un-
conscious, such as those which occur during sleep or anaesthesia, or which
affect our otherwise insensitive internal organs.

LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE 29

A further instance of nerve-regulation is seen in secreting glands. Not
all glands are thus regulated, at least not directly ; but in those which are,

the effects are striking. Their regulation is of the same
Regulation of general nature as that exercised upon involuntary

muscle, but it influences the chemical activities of the
gland-cells and the outpouring of secretion from them.
By means of this regulation a secretion can be produced or arrested,
increased or diminished. As with muscle, a suitable balance is in this
way maintained, and the activity of the glands is adapted to the require-
ments of the organism. Most of the digestive glands are thus influenced,
as are the skin-glands which secrete sweat. And by the action of the

nervous system upon the skin-glands, together with its
effect in increasing or diminishing the blood-supply to
the cutaneous blood-vessels, the temperature of our
blood is regulated and is kept at the point best suited for maintenance of
the life and activity of the tissues.

The action of the nervous system upon the secretion of glands is
strikingly exemplified, as in the case of its action upon the heart and

blood-vessels by the effects of the emotions. Thus an
emotion of one kind such as the anticipation of food-
will cause saliva to flow ' the mouth to water ' ;
whereas an emotion of another kind such as fear or anxiety will stop
the secretion, causing the 'tongue to cleave unto the roof of the mouth,'
and rendering speech difficult or impossible. Such arrest of the salivary
secretion also makes the swallowing of dry food difficult : advantage of
this fact is taken in the ' ordeal by rice ' which used to be employed in the
East for the detection of criminals.

The activities of the cells constituting our bodies are controlled, as
already mentioned, in another way than through the nervous system,

viz., by chemical agents (hormones) circulating in the

f*. m , * * V ^J * *-J

chemical^ gents : blood. Many of these are produced by special glandular
hormones, internal organs, known as internally secreting glands. The
secretions. ordinary secreting glands pour their secretions on the

exterior of the body or on a surface communicating with the exterior ; the
internally secreting glands pass the materials which they produce directly
into the blood. In this fluid the hormones are carried to distant organs.
Their influence upon an organ may be essential to the proper performance
of its functions or may be merely ancillary to it. In the former case
removal of the internally secreting gland which produces the hormone, or
its destruction by disease, may prove fatal to the organism. This is the

case with the suprarenal capsules : small glands which
Suprarenals. are a( jj acen t to t h e kidneys, although having no

physiological connection with these organs. A Guy's physician, Dr.
Addison, in the middle of the last century showed that a certain affection,
almost always fatal, since known by his name, is associated with disease

30 LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE

of the suprarenal capsules. A short time after this observation a French
physiologist, Brown- Sequard, found that animals from which the supra-
renal capsules are removed rarely survive the operation for more than a
few days. In the concluding decade of the last century interest in these
bodies was revived by the discovery that they are constantly yielding to
the blood a chemical agent (or hormone) which stimulates the contractions
of the heart and arteries and assists in the promotion of every action
which is brought about through the sympathetic nervous system (Lang-
ley). In this manner the importance of their integrity has been explained,
although we have still much to learn regarding their functions.

Another instance of an internally secreting gland which is essential
to life, or at least to its maintenance in a normal condition, is the thyroid.

The association of imperfect development or disease
of the thyroid with disorders of nutrition and inactivity
of the nervous system is well ascertained. The form of idiocy known as
cretinism and the affection termed myxoedema are both associated with
deficiency of its secretion : somewhat similar conditions to these are
produced by the surgical removal of the gland. The symptoms are
alleviated or cured by the administration of its juice. On the other
hand, enlargement of the thyroid, accompanied by increase of its secre-
tion, produces symptoms of nervous excitation, and similar symptoms
are caused by excessive administration of the glandular substance by
the mouth. From these observations it is inferred that the juice contains
hormones which help to regulate the nutrition of the body and serve
to stimulate the nervous system, for the higher functions of which they
appear to be essential. To quote M. Gley, to whose researches we
owe much of our knowledge regarding the functions of this organ : * La
genese et 1'exercice des plus hautes faculte's de 1'homme sont conditionne"s
par 1' action purement chimique d'un produit de se'cre'tion. Que les
psychologues me"ditent ces faits ! '

The case of the parathyroid glandules is still more remarkable.
These organs were discovered by Sandstrom in 1880. They are four

minute bodies, each no larger than a pin's head,
imbedded in the thyroid. Small as they are, their
internal secretion possesses hormones which exert a powerful influence
upon the nervous system. If they are completely removed, a complex
of symptoms, technically known as ' tetany,' is liable to occur, which
is always serious and may be fatal. Like the hormones of the thyroid
itself, therefore, those of the parathyroids produce effects upon the
nervous system, to which they are carried by the blood ; although the
effects are of a different kind.

Another internally secreting gland which has evoked considerable
interest during the last few years is the pituitary body. This is a small
structure no larger than a cob-nut attached to the base of the brain.
It is mainly composed of glandular cells. Its removal has been found (by

LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE 31

most observers) to be fatal often within two or three days. Its hyper-
trophy, when occurring during the general growth of the body, is attended

by an undue development of the skeleton, so that
Pituitary. n ,. ,.

the stature tends to assume gigantic proportions.

When the hypertrophy occurs after growth is completed, the extremities
-viz., the hands and feet and the bones of the face are mainly affected ;
hence the condition has been termed ' acromegaly ' (enlargement of
extremities). The association of this condition with affections of the
pituitary was pointed out in 1885 by a distinguished French physician,
Dr. Pierre Marie. Both ' giants ' and ' acromegalists ' are almost in-
variably found to have an enlarged pituitary. The enlargement is
generally confined to one part the anterior lobe and we conclude
that this produces hormones which stimulate the growth of the body
generally and of the skeleton in particular. The remainder of the
pituitary is different in structure from the anterior lobe and has a
different function. From it hormones can be extracted which, like those
of the suprarenal capsule, although not exactly in the same manner,
influence the contraction of the heart and arteries. Its extracts are also
instrumental in promoting the secretion of certain glands. When
injected into the blood they cause a free secretion of water from the
kidneys and of milk from the mammary glands, neither of which organs
are directly influenced (as most other glands are) through the nervous
system. Doubtless under natural conditions these organs are stimulated
to activity by hormones which are produced in the pituitary and which
pass from this into the blood.

The internally secreting glands which have been mentioned (thyroid,
parathyroid, suprarenal, pituitary) have, so far as is known, no other
function than that of producing chemical substances of this character
for the influencing of other organs, to which they are conveyed by the
blood. It is interesting to observe that these glands are all of very small
size, none being larger than a walnut, and some the parathyroids
almost microscopic. In spite of this, they are essential to the proper
maintenance of the life of the body, and the total removal of any of them
by disease or operation is in most cases speedily fatal.

There are, however, organs in the body yielding internal secretions
to the blood in the shape of hormones, but exercising at the same time

other functions. A striking instance is furnished by
the pancreas, the secretion of which is the most
important of the digestive juices. This the pancreatic juice forms the
external secretion of the gland, and is poured into the intestine, where its
action upon the food as it passes out from the stomach has long been
recognised. It was, however, discovered in 1889 by von Mering and Min-
kowski that the pancreas also furnishes an internal secretion, containing
a hormone which is passed from the pancreas into the blood, by which
it is carried first to the liver and afterwards to the body generally. This

32 LIFE: ITS NATUEE, ORIGIN AND MAINTENANCE

hormone is essential to the proper utilisation of carbohydrates in the
organism. It is well known that the carbohydrates of the food are
converted into grape sugar and circulate in this form in the blood, which
always contains a certain amount ; the blood conveys it to all the cells
of the body, and they utilise it as fuel. If, owing to disease of the pan-
creas or as the result of its removal by surgical procedure, its internal
secretion is not available, sugar is no longer properly utilised by the cells
of the body and tends to accumulate in the blood ; from the blood the
excess passes off by the kidneys, producing diabetes.

Another instance of an internal secretion furnished by an organ which
is devoted largely to other functions is the ' pro-secretin ' found in the

cells lining the duodenum. When the acid gastric

Duodenum. . . . . , , MM. i.

juice comes into contact with these cells it converts

their pro-secretin into ' secretin.' This is a hormone which is passed into
the blood and circulates with that fluid. It has a specific effect on the
externally secreting cells of the pancreas, and causes the rapid outpouring
of pancreatic juice into the intestine. This effect is similar to that of the
hormones of the pituitary body upon the cells of the kidney and mammary
gland. It was discovered by Bayliss and Starling.

The reproductive glands furnish in many respects the most interesting
example of organs which besides their ordinary products, the germ- and
Internal secretions sperm-cells (ova and spermatozoa) form hormones
of the reproductive which circulate in the blood and effect changes in cells
organs. o f distant parts of the body. It is through these

hormones that the secondary sexual characters, such as the comb and tail
of the cock, the mane of the lion, the horns of the stag, the beard and
enlarged larynx of a man, are produced, as well as the many differences in
form and structure of the body which are characteristic of the sexes. The
dependence of these so-called secondary sexual characters upon the state
of development of the reproductive organs has been recognised from time
immemorial, but has usually been ascribed to influences produced through
the nervous system, and it is only in recent years that the changes have
been shown to be brought about by the agency of internal secretions
and hormones, passed from the reproductive glands into the circulating
blood.*

It has been possible in only one or two instances to prepare and isolate
the hormones of the internal secretions in a sufficient condition of purity to

subject them to analysis, but enough is known about
f them to indicate that they are organic bodies of a not
very complex nature, far simpler than proteins and
even than enzymes. Those which have been studied are all dialysable,
are readily soluble in water but insoluble in alcohol, and are not destroyed
by boiling. One at least that of the medulla of the suprarenal capsule-

* The evidence is to be found in F. H. A. Marshall, The Physiology of Reproduction,
1911.

LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE 33

has been prepared synthetically, and when their exact chemical nature
has been somewhat better elucidated it will probably not be difficult to
obtain others in the same way.

From the above it is clear that not only is a co-ordination through the
nervous system necessary in order that life shall be maintained in a
normal condition, but a chemical co-ordination is no less essential. These
may be independent of one another ; but on the other hand they may
react upon one another. For it can be shown that the production of
some at least of the hormones is under the influence of the nervous
system (Biedl, Asher, Elliott) ; whilst, as we have seen, some of the
functions of the nervous system are dependent upon hormones.

Time will not permit me to refer in any but the briefest manner to
the protective mechanisms which the cell-aggregate has evolved for its
Protective chemical defence against disease, especially disease produced
mechanisms. Toxins by parasitic micro-organisms. These, which with
an antitoxins. ew exce pti O ns are unicellular, are without doubt the

most formidable enemies which the multicellular Metazoa, to which all
the higher animal organisms belong, have to contend against. To such
micro-organisms are due inter alia all diseases which are liable to become
epidemic, such as anthrax and rinderpest in cattle, distemper in dogs and
cats, small-pox, scarlet fever, measles, and sleeping sickness in man. The
advances of modern medicine have shown that the symptoms of these
diseases the disturbances of nutrition, the temperature, the lassitude or
excitement, and other nervous disturbances are the effects of chemical
poisons (toxins) produced by the micro-organisms and acting deleteriously
upon the tissues of the body. The tissues, on the other hand, endeavour
to counteract these effects by producing other chemical substances
destructive to the micro-organisms or antagonistic to their action : these
are known as anti-bodies. Sometimes the protection takes the form of a
subtle alteration in the living substance of the cells which renders them
for a long time, or even permanently, insusceptible (immune) to the action
of the poison. Sometimes certain cells of the body, such as the white
corpuscles of the blood, eat the invading micro-organisms and destroy
them bodily by the action of chemical agents within their protoplasm.
The result of an illness thus depends upon the result of the struggle
between these opposing forces the micro-organisms on the one hand
and the cells of the body on the other both of which fight with
chemical weapons. If the cells of the body do not succeed in destroy-
ing the invading organisms it is certain that the invaders will in the
long run destroy them, for in this combat no quarter is given. For-
tunately we have been able, by the aid of animal experimentation,
to acquire some knowledge of the manner in which we are attacked
by micro-organisms and of the methods which the cells of our body
adopt to repel the attack, and the knowledge is now extensively utilised
to assist our defence. For this purpose protective serums or anti-

3

34 LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE

toxins, which have been formed in the blood of other animals, are
employed to supplement the action of those which our own cells
produce. It is not too much to assert that the knowledge of the
parasitic origin of so many diseases and of the chemical agents which

on the one hand cause, and on the other combat, their
diseased na ure symptoms, has transformed medicine from a mere art

practised empirically into a real science based upon
experiment. The transformation has opened out an illimitable vista
of possibilities in the direction not only of cure, but, more important
still, of prevention. It has taken place within the memory of most of us
who are here present. And only last February the world was mourning
the death of one of the greatest of its benefactors a former President of
this Association * who, by applying this knowledge to the practice of
surgery, was instrumental, even in his own lifetime, in saving more
lives than were destroyed in all the bloody wars of the nineteenth
century !

The question has been debated whether, if all accidental modes of
destruction of the life of the cells could be eliminated, there would

remain a possibility of individual cell-life, and even of
aggregate cell-life, continuing indefinitely; in other
words, Are the phenomena of senescence and death a
natural and necessary sequence to the existence of life ? To most of my
audience it will appear that the subject is not open to debate. But some
physiologists (e.g., Metchnikoff) hold that the condition of senescence
is itself abnormal ; that old age is a form of disease or is due to disease,
and, theoretically at least, is capable of being eliminated. We have
already seen that individual cell-life, such as that of the white blood-
corpuscles and of the cells of many tissues, can under suitable con-
ditions be prolonged for days or weeks or months after general death.
Unicellular organisms kept under suitable conditions of nutrition have
been observed to carry on their functions normally for prolonged periods
and to show no degeneration such as would accompany senescence.
They give rise by division to others of the same kind, which also, under
favourable conditions, continue to live, to all appearance indefinitely.
But these instances, although they indicate that in the simplest forms
of organisation existence may be greatly extended without signs of
decay, do not furnish conclusive evidence of indefinite prolongation of
life. Most of the cells which constitute the body, after a period
of growth and activity, sometimes more, sometimes less prolonged,
eventually undergo atrophy and cease to perform satisfactorily the
functions which are allotted to them. And when we consider the body
as a whole, we find that in every case the life of the aggregate consists
of a definite cycle of changes which, after passing through the stages
of growth and maturity, always leads to senescence, and finally
* Lord Lister was President at Liverpool in 1896.

LIFE: ITS NATUEE, OEIGIN AND MAINTENANCE 35

terminates in death. The only exception is in the reproductive cells,
in which the processes of maturation and fertilisation result in rejuvenes-
cence, so that instead of the usual downward change towards senes-
cence, the fertilised ovum obtains a new lease of life, which is carried
on into the new-formed organism. The latter again itself ultimately
forms reproductive cells, and thus the life of the species is continued. It
is only in the sense of its propagation in this way from one generation to
another that we can speak of the indefinite continuance of life : we can
only be immortal through our descendants !

The individuals of every species of animal appear to have an average
duration of existence.* Some species are known the individuals of

which live only for a few hours, whilst others survive
Average duration of f or a hundred years.! In man himself the average

length of life would probably be greater than the
three-score and ten years allotted to him by the
Psalmist if we could eliminate the results of disease and accident ; when
these results are included it falls far short of that period. If the terms of
life given in the purely mythological part of the Old Testament were
credible, man would in the early stages of his history have possessed
a remarkable power of resisting age and disease. But, although maoy
here present were brought up to believe in their literal veracity, such
records are no longer accepted even by the most orthodox of theolo-
gians, and the nine hundred odd years with which Adam and his
immediate descendants are credited, culminating in the nine hundred
and sixty-nine of Methuselah, have been relegated, with the account of
Creation and the Deluge, to their proper position in literature. When
we come to the Hebrew Patriarchs, we notice a considerable diminu-
tion to have taken place in what the insurance offices term the ' expec-
tation of life.' Abraham is described as having lived only to 175
years, Joseph and Joshua to 110, Moses to 120 ; even at that age
' his eye was not dim nor his natural force abated.' We cannot say
that under ideal conditions all these terms are impossible ; indeed,
Metchnikoff is disposed to regard them as probable ; for great ages are
still occasionally recorded, although it is doubtful if any as consider-
able as these are ever substantiated. That the expectation of life was
better then than now would be inferred from the apologetic tone adopted
by Jacob when questioned by Pharaoh as to his age : ' The days of the
years of my pilgrimage are an hundred and thirty years ; few and evil
have the days of the years of my life been, and have not attained unto
the days of the years of the life of my fathers in the days of their

* This was regarded by Buffon as related to the period of growth, but the ratio is
certainly not constant. The subject is discussed by Kay Lankester in an early work :
On Comparative Longevity in Man and Animals, 1870.

f The approximately regular periods of longevity of different species of animals
furnishes a strong argument against the theory that the decay of old age is an
accidental phenomenon, comparable with disease.

36 LIFE: ITS NATURE, ORIGIN AND MAINTENANCE

pilgrimage.' David, to whom, before the advent of the modern statis-
tician, we owe the idea that seventy years is to be regarded as the
normal period of life,* is himself merely stated to have ' died in a good
old age.' The periods recorded for the Kings show a considerable
falling-off as compared with the Patriarchs ; but not a few were cut off by
violent deaths, and many lived lives which were not ideal. Amongst
eminent Greeks and Romans few very long lives are recorded, and the
same is true of historical persons in mediaeval and modern history. It
is a long life that lasts much beyond eighty; three such linked together
carry us far back into history. Mankind is in this respect more favoured
than most mammals, although a few of these surpass the period of man's
existence.! Strange that the brevity of human life should be a favourite
theme of preacher and poet when the actual term of his ' erring
pilgrimage ' is greater than that of most of his fellow-creatures !

The modern applications of the principles of preventive medicine and
hygiene are no doubt operating to lengthen the average life. But even

if the ravages of disease could be altogether eliminated,
The end of life. ... . ,, , ,, ,, , , ,

it is certain that at any rate the fixed cells of our body

must eventually grow old and ultimately cease to function ; when this
happens to cells which are essential to the life of the organism, general
death must result. This will always remain the universal law, from
which there is no escape. ' All that lives must die, passing through
nature to eternity ! '

Such natural death unaccelerated by disease is not death by disease
as unnatural as death by accident ? should be a quiet, painless phe-
nomenon, unattended by violent change. As Dastre expresses it, 'The
need of death should appear at the end of life, just as the need of sleep
appears at the end of the day.' The change has been led gradually up
to by an orderly succession of phases, and is itself the last manifestation
of life. Were we all certain of a quiet passing were we sure that there
would be ' no moaning of. the bar when we go out to sea ' we could
anticipate the coming of death after a ripe old age without apprehension.
And if ever the time shall arrive when man will have learned to regard
this change as a simple physiological process, as natural as the oncoming
of sleep, the approach of the fatal shears will be as generally welcomed
as it is now abhorred. Such a day is still distant ; we can hardly say
that its dawning is visible. Let us at least hope that, in the manner
depicted by Diirer in his well-known etching, the sunshine which science
irradiates may eventually put to flight the melancholy which hovers, bat-
like, over the termination of our lives, and which even the anticipation of
a future happier existence has not hitherto succeeded in dispersing.

* The expectation of life of a healthy man of fifty is still reckoned at about twenty
years.

f ' Hominis sevum cseterorum animalium omnium superat praeter admodum
paucoruin. ' Francis Bacon, Historic/, vita et mortis, 1637. ^

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