acquainted with all facts which are supposed to prove the inheritance
of acquired characters,—that is of characters which are not due to
the peculiar organization of the ovum and spermatozoon from which the
individual is formed, but which follow from the incidence of
accidental external influences upon the organism at any time in its
life. Not one of these facts can be accepted as a proof of the
transmission of acquired characters.’ _l. c._ p. 68.
Footnote 43:
‘Physiologie der Zeugung.’
Footnote 44:
See ‘Ueber die Uebung,’ Berlin, 1881.
Footnote 45:
This principle was, I believe, first pointed out by Seidlitz. Compare
Seidlitz, ‘Die Darwin’sche Theorie,’ Leipzig, 1875, p. 198.
Footnote 46:
W. Roux, ‘Der Kampf der Theile im Organismus,’ Leipzig, 1881.
Footnote 47:
Compare Born in ‘Zoolog. Anzeiger,’ 1883, No. 150, p. 537.
Footnote 48:
O. C. Marsh, ‘Odontornithes, a Monograph on the extinct toothed Birds
of North America,’ Washington, 1880.
Footnote 49:
C. Darwin, ‘Variation of Animals and Plants under Domestication.’
Vol. I.
Footnote 50:
Compare ‘Der thierische Wille,’ Leipzig, 1880.
Footnote 51:
Steller’s interesting account of the Sea-cow (_Rhytina Stelleri_)
proves that this suggestion is valid. This large mammal was living in
great numbers in Behring Strait at the end of the last century, but
has since been entirely exterminated by man. Steller, who was
compelled by shipwreck to remain in the locality for a whole year,
tells us that the animals were at first without any fear of man, so
that they could be approached in boats and could thus be killed.
After a few months however the survivors became wary, and did not
allow Steller’s men to approach them, so that they were difficult to
catch.—A. W., 1888.
Footnote 52:
Compare Schneider, ‘Der thierische Wille.’
Footnote 53:
[The author refers to the Academy of Arts at Munich. S. S.]
Footnote 54:
Compare Darwin’s ‘Descent of Man.’
Footnote 55:
‘Studien zur Descendenztheorie, I. Ueber den Saison-Dimorphismus der
Schmetterlinge.’ Leipzig, 1875. English edition translated and edited
by Professor Meldola, ‘Studies in the Theory of Descent,’ Part I.
Footnote 56:
The colours which have been called forth by sexual selection must
also be included here.
Footnote 57:
Wilhelm Roux, ‘Der Kampf der Theile im Organismus.’ Leipzig, 1881.
Footnote 58:
Consult ‘Studien zur Descendenztheorie, IV. Über die mechanische
Auffassung der Natur,’ p. 303, etc. Translated and edited by
Professor Meldola; see ‘Studies in the Theory of Descent,’ p. 677, &c.
------------------------------------------------------------------------
III.
LIFE AND DEATH.
1883.
------------------------------------------------------------------------
LIFE AND DEATH.
PREFACE.
The following paper was first printed as an academic lecture in the
summer of the present year (1883), with the title ‘Upon the Eternal
Duration of Life’ (‘Über die Ewigkeit des Lebens’). In now bringing it
before a larger public in an expanded and improved form, I have chosen
a title which seemed to me to correspond better with the present
contents of the paper.
The stimulus which led to this biological investigation was given in a
memoir by Götte, in which this author opposes views which I had
previously expressed. Although such an origin has naturally caused my
paper to take the form of a reply, my intention was not merely to
controvert the views of my opponent, but rather—using those opposed
views as a starting-point—to throw new light upon certain questions
which demand consideration; to give additional support to thoughts
which I have previously expressed, and to penetrate, if possible, more
deeply into the problem of life and death.
If, in making this attempt, the views of my opponent have been severely
criticized, it will be acknowledged that the criticisms do not form the
purpose of my paper, but only the means by which the way to a more
correct understanding of the problems before us may be indicated.
A. W.
Freiburg i. Breisgau,
_Oct. 18, 1883_.
------------------------------------------------------------------------
III.
LIFE AND DEATH.
In the previous essay, entitled ‘The Duration of Life,’ I have
endeavoured to show that the limitation of life in single individuals
by death is not, as has been hitherto assumed, an inevitable
phenomenon, essential to the very nature of life itself; but that it is
an adaptation which first appeared when, in consequence of a certain
complexity of structure, an unending life became disadvantageous to the
species. I pointed out that we could not speak of natural death among
unicellular animals, for their growth has no termination which is
comparable with death. The origin of new individuals is not connected
with the death of the old; but increase by division takes place in such
a way that the two parts into which an organism separates are exactly
equivalent one to another, and neither of them is older or younger than
the other. In this way countless numbers of individuals arise, each of
which is as old as the species itself, while each possesses the
capability of living on indefinitely, by means of division.
I suggested that the Metazoa have lost this power of unending life by
being constructed of numerous cells, and by the consequent division of
labour which became established between the various cells of the body.
Here also reproduction takes place by means of cell-division, but every
cell does not possess the power of reproducing the whole organism. The
cells of the organism are differentiated into two essentially different
groups, the reproductive cells—ova or spermatozoa, and the somatic
cells, or cells of the body, in the narrower sense. The immortality of
the unicellular organism has only passed over to the former; the others
must die, and since the body of the individual is chiefly composed of
them, it must die also.
I have endeavoured to explain this fact as an adaptation to the general
conditions of life. In my opinion life became limited in its duration,
not because it was contrary to its very nature to be unlimited, but
because an unlimited persistence of the individual would be a luxury
without a purpose. Among unicellular organisms natural death was
impossible, because the reproductive cell and the individual were one
and the same: among multicellular animals it was possible, and we see
that it has arisen.
Natural death appeared to me to be explicable on the principle of
utility, as an adaptation.
These opinions, to which I shall return in greater detail in a later
part of this paper, have been opposed by Götte[59], who does not
attribute death to utility, but considers it to be a necessity inherent
in life itself. He considers that it occurs not only in the Metazoa or
multicellular animals, but also in unicellular forms of life, where it
is represented by the process of encystment, which is to be regarded as
the death of the individual. This encystment is a process of
rejuvenescence, which, after a longer or shorter interval, interrupts
multiplication by means of fission. According to Götte, this process of
rejuvenescence consists in the dissolution of the specific structure of
the individual, or in the retrogression of the individual to a form of
organic matter which is no longer living but which is comparable to the
yolk of an egg. This matter is, by means of its internal energy, and in
consequence of the law of growth which is inherent in its constitution,
enabled to give rise to a new individual of the same species.
Furthermore, the process of rejuvenescence among unicellular beings
corresponds to the formation of germs in the higher organisms. The
phenomena of death were transmitted by heredity from the unicellular
forms to the Metazoa when they arose. Death does not therefore appear
for the first time in the Metazoa, but it is an extremely ancient
process which ‘goes back to the first origin of organic beings’ (l. c.,
p. 81).
It is obvious, from this short _résumé_, that Götte’s view is totally
opposed to mine. Inasmuch as only one of these views can be
fundamentally right, it is worth while to compare the two; and although
we cannot at present hope to explain the ultimate physiological
processes which involve life and death, I think nevertheless that it is
quite possible to arrive at definite conclusions as to the general
causes of these phenomena. At any rate, existing facts have not been so
completely thought out that it is useless to consider them once more.
The question—what do we understand by death? must be decided before we
can speak of the origin of death. Götte says, ‘we are not able to
explain this general expression quite definitely and in all its
details, because the moment of death, or perhaps more exactly the
moment when death is complete, can in no case be precisely indicated.
We can only say that in the death of the higher animals, all those
phenomena which make up the life of the individual cease, and further
that all the cells and elements of tissue which form the dead organism,
die, and are resolved into their elements.’
This definition would suffice if it did not include that which is to be
defined. For it assumes that under the expression ‘dead organism’ we
must include those organisms which have brought to an end the whole of
their vital functions, but of which the component cells and elements
may still be living. This view is afterwards more accurately explained,
and in fact there is no doubt that the cessation of the activity of
life in the multicellular organism rarely implies any direct connection
with the cessation of vital functions in all its constituents. The
question however arises, whether it is right or useful to limit the
conception of death to the cessation of the functions of the organism.
Our conceptions of death have been derived from the higher organisms
alone, and hence it is quite possible that the conception may be too
limited. The limitation might perhaps be removed by accurate and
scientific comparison with the somewhat corresponding phenomena among
unicellular organisms, and we might then arrive at a more comprehensive
definition. Science has without doubt the right to make use of popular
terms and conceptions, and by a more profound insight to widen or
restrict them. But the main idea must always be retained, so that
nothing quite new or strange may appear in the widened conception. The
conception of death, as it has been expressed with perfect uniformity
in all languages, has arisen from observations on the higher animals
alone; and it signifies not only the cessation of the vital functions
of the whole organism, but at the same time the cessation of life in
its single parts, as is shown by the impossibility of revival. The
_post-mortem_ death of the cells is also part of death, and was so,
long before science established the fact that an organism is built up
of numerous very minute living elements, of which the vital processes
partially continue for some time after the cessation of those of the
whole organism. It is precisely this incapacity on the part of the
organism to reproduce the phenomena of life anew, which distinguishes
genuine death from the arrest of life or trance; and the incapacity
depends upon the fact that the death of the cells and tissues follows
upon the cessation of the vital functions as a whole. I would, for this
reason, define death as an arrest of life, from which no lengthened
revival, either of the whole or any of its parts, can take place; or,
to put it concisely, as a definite arrest of life. I believe that in
this definition I have expressed the exact meaning of the conception
which language has sought to convey in the word death. For our present
purpose, the cause which gives rise to this phenomenon is of no
importance,—whether it is simultaneous or successive in the various
parts of the organism, whether it makes its appearance slowly or
rapidly. For the conception itself it is also quite immaterial whether
we are able to decide if death has really taken place in any particular
case; however uncertain we might be, the state which we call death
would be not less sharply and definitely limited. We might consider the
caterpillar of _Euprepia flavia_ to be dead when frozen in ice, but if
it recovered after thawing and became an imago, we should say that it
had only been apparently dead, that life stood still for a time, but
had not ceased for ever. It is only the irretrievable loss of life in
an organism which we call death, and we ought to hold fast to this
conception, so that it will not slip from us, and become worthless,
because we no longer know what we mean by it.
We cannot escape this danger if we look upon the _post-mortem_ death of
the cells of the body as a phenomenon which may accompany death, but
which may sometimes be wanting. An experiment might be made in which
some part of a dead animal, such as the comb of a cock, might be
transplanted, before the death of the cells, to some other living
animal: such a part might live in its new position, thus showing that
single members may survive after the appearance of death, as I
understand it. But the objection might be raised that in such a case
the cock’s comb has become a member of another organism, so that it
would be lost labour to insert a clause in our definition of death
which would include this phenomenon. The same objection might be raised
if the transplantation took place a day or even a year before the death
of the cock.
Götte is decidedly in error when he considers that the idea of death
merely expresses an ‘arrest of the sum of vital actions in the
individual,’ without at the same time including that definite arrest
which involves the impossibility of any revival. Decomposition is not
quite essential to our definition, inasmuch as death may be followed by
drying-up[60], or by perpetual entombment in Siberian ice (as in the
well-known case of the mammoth), or by digestion in the stomach of a
beast of prey. But the notion of a dead body is indeed inseparably
connected with that of death, and I believe that I was right in
distinguishing between the division of an Infusorian into two
daughter-cells, and the death of a Metazoon, which leaves offspring
behind it, by calling attention to the absence of a dead body in the
process of fission among Infusoria (See below.). The real proof of
death is that the organized substance which previously gave rise to the
phenomena of life, for ever ceases to originate such phenomena. This,
and this alone, is what mankind has hitherto understood by death, and
we must start from this definition if we wish to retain a firm basis
for our considerations.
We must now consider whether this definition, derived from observation
of higher animals, may be also applied without alteration to the lower,
or whether the corresponding phenomena which arise in these latter,
differ in detail from those of the higher animals, so that a narrower
limitation of the above definition is rendered necessary.
Götte believes the process of encystment which takes place in so many
unicellular animals (Monoplastides) to be the analogue of death.
According to this authority, the individuals in question, not only
undergo a kind of winter sleep—a period of latent life—but when
surrounded by the cyst they lose their former specific organization;
they become a ‘homogeneous substance,’ and are resolved into a germ,
from which, by a process of development, a new individual of the same
species once more arises. The division of the contents of the cyst,
viz. its multiplication, is, according to this view, of secondary
importance, and the essential feature in the process is the
rejuvenescence of the individual. This rejuvenescence however is said
to not only consist in the simple transformation of the old individual,
but in its death, followed by the building up anew of another
individual. ‘The parent organism and its offspring are two successive
living stages of the same substance—separated, and at the same time
connected, by the condition of rejuvenescence which lies between them’
(l. c., p. 79). An ‘absolute continuity of life does not exist’; it is
only the dead organic matter which establishes the connection, and the
‘identity of this matter ensures heredity.’
It is certainly surprising that Götte should identify encystment with a
cessation of life, and we may well inquire for the evidence which is
believed to support such a view. The only evidence lies in a certain
degree of degeneration in the structure of the individual, and in the
cessation of the visible external phenomena of life, such as feeding
and moving. Does Götte really believe that it is an incorrect
interpretation of the facts to assume that a _vita minima_ continues to
exist in the protoplasm, after its complexity has diminished? Are we
compelled to invoke a mystical explanation of the facts, by an appeal
to such an indefinite principle as Götte’s rejuvenescence? Would not
the oxygen, dissolved in the water, affect the organic substance the
life of which it formerly maintained, and would it not cause its
decomposition, if it were in reality dead?
I, too, hold that the division of the encysted mass is of secondary
importance, and that the encystment itself, without the resulting
multiplication, is the original and essential part of the phenomenon.
But it does not follow from this that the encystment should be
considered as a process of rejuvenescence. What is there to be
rejuvenated? Certainly not the substance of the animal, for nothing is
added to it, and it can therefore acquire no new energy; and the forms
of energy which it manifests cannot be changed, since the form of the
matter is just the same after quitting the cyst as it was before.
Rejuvenescence has also been mentioned in connection with the process
of conjugation, but this is quite another thing. It is quite
reasonable, at least in a certain sense, to maintain the connection of
rejuvenescence with conjugation; for a fusion of the substance of two
individuals takes place, to a greater or lesser extent, in conjugation,
and the matter which composes each individual is therefore really
altered. But in simple encystment, rejuvenescence can only be
understood in the sense in which we speak of the fable of the Phœnix,
which, when old, was believed to be consumed by fire, and to rise again
from its own ashes as a young bird. I doubt whether this idea is in
agreement with the physiology of to-day, or with the laws of the
conservation of energy. It is easy to pull down an old house with
rotten beams and crumbling walls, but it would be impossible to build
it anew with the old material, even if we used new mortar, represented
in Götte’s hypothesis by water and oxygen. For these reasons I consider
the idea of rejuvenescence of the encysted individual to be contrary to
our present physiological knowledge.
It is much more simple and natural to regard encystment as adapted for
the protection of certain individuals in a colony from destruction by
being dried up or frozen, or for the protection of the individual
during multiplication by division, when it is helpless, and would
easily fall a prey to enemies, or to secure advantages in some other
way[61]. The case of _Actinosphaerium_, mentioned by Götte, clearly
demonstrates that rejuvenescence of the individual is not the only
event which happens during encystment, for this would scarcely require
six months. The long duration of latent life, from summer to the next
spring, clearly proves that encystment is of the highest importance for
the species, in order to maintain the life of the individual through
the dangers of an unfavourable season[62].
When in this case, the specific organization degenerates to a certain
extent, such changes depend in part upon the endeavour to diminish as
far as possible the size of the organism—the pseudopodia being drawn
in, while the vacuoles contract and completely disappear. The
degeneration may also, perhaps, depend in part upon the secretion of
the cyst itself, which implies a certain loss of substance[63]. But
degeneration chiefly depends upon the fact that the encystment is
accompanied by reproduction in the way of fission, which seems to begin
with a simplification of the organization, that is, with a fusion of
the numerous nuclei. It is well known that many unicellular animals
contain several nuclei—in other words, that the nuclear substance is
scattered in small parts throughout the whole cell. But when the animal
prepares for division, these pieces of nuclear substance fuse into a
single nucleus which itself undergoes division into two equal parts[64]
during the division of the animal. It is evident that the equal
division of the whole nuclear substance only becomes possible in this
way.
There are, however, numerous cases which prove that the bodies of
encysted animals may retain, during the whole process, exactly the same
structure and differentiation, which were previously characteristic of
them. Thus the large Infusorian _Tillina magna_, described by Gruber,
can be seen through the thin-walled cyst to retain the characteristic
structure of its ectoplasm, and the whole of its organization. Even the
movements of the enclosed animal do not cease; it continues to rotate
actively in the narrow cyst, as do the two or four parts into which it
subsequently divides. Such observations prove that Götte’s view that
‘every characteristic of the previous organization is lost,’ is quite
out of the question[65] (l. c., p. 62).
For this reason I must strongly oppose Götte’s view that an encysted
individual is a germ, viz. an organic mass still unorganized which can
only become an adult individual by means of a process of development. I
believe that an encysted individual is one possessing a protective
membrane, in structure more or less simplified as an adaptation to the
narrow space within the cyst, and to a possible subsequent increase by
division, in short one in which active life is reduced to a minimum,
and sometimes even completely in abeyance, as happens when it is frozen.
It is evident from the above considerations that encystment in no way
corresponds with that which every one, including myself, understands by
death, because during encystment one and the same being is first
apparently dead and then again alive; and we merely witness a condition
of rest, from which active life will again emerge. This would remain
true even if it were proved that life is, in reality, suspended for a
time. But such proof is still wanting, and Götte was apparently only
influenced by theoretical considerations, when he imagined that death
intervened where unprejudiced observers have only recognised a
condition of rest. He apparently entirely overlooked the fact that it
is possible to test his views; for all unicellular beings are in
reality capable of dying: we can kill them, for example, by boiling,
and they are then really dead and cannot be revived. But this state of
the organism differs chemically and physically from the encysted
condition, although we do not know all the details of the difference.
The encysted animal, when placed in fresh water, presently originates a
living individual, but the one killed by boiling only results in
decomposition of the dead organic matter. Hence we see that the same
external conditions give rise to different results in two different
states of the organism. It cannot be right to apply the same term to
two totally different states. There is only one phenomenon which can be
called death, although it may be produced by widely different causes.
But if the encysted condition is not identical with the death which we
can produce at will, then natural death, viz. that arising from
internal causes, does not exist at all among unicellular organisms.
These facts refute Götte’s peculiar view, which depends on the
existence of natural death among the Monoplastid organisms; upon proof
of the contradictory, his whole theory collapses. But there is
nevertheless a certain interest in following it further, for we shall
thus reach many ideas worthy of consideration.