INVESTIGATIONS ON NATURAL DEATH
I
NATURAL DEATH AMONG PLANTS
Theory of the immortality of unicellular
organisms—Examples of very old trees—Examples of
short-lived plants—Prolongation of the life of some
plants—Theory of the natural death of plants by
exhaustion—Death of plants from auto-intoxication
It must surprise my readers to find how little science really knows
about death. Although death has a preponderating place in religions,
systems of philosophy, literature and folk-lore, scientific works pay
little attention to it. This unfortunate fact explains, although it may
not justify, the bitter attack made on science on the grounds that it
is occupied with minutiæ and neglects the great problems of human life,
such as death. When Tolstoi was absorbed by the problem and searched
for some solution in the writings of scientific men, he found that the
explanations were trivial or inexact. In consequence he was extremely
indignant with the men who devoted themselves to the investigation of
what seemed to him useless problems (such as the insect world, or the
structure of cells and tissues) and who were yet unable to say what the
destiny of man or death might be.
I am far from claiming to solve these problems; I can do little more
than describe the actual state of the question of natural death. I hope
in this way at least to prepare for scientific investigation, and to
call attention to it as the most important problem of humanity.
By the use of the phrase “natural death” I mean to denote a phenomenon
that is intrinsic in the nature of an organism and that is not the mere
result of an external accident. Popular phraseology includes under
natural death all cases due to diseases. But as such deaths can be
avoided and are not due to qualities inherent in the organism, it is
erroneous to include them in the category “natural death.”
In nature, death comes so frequently by accident that there is
justification for asking if natural death really occurs. It used to be
thought that death was the inevitable end of life and that the living
principle contained within itself the germ of death. Accordingly,
it was a surprising discovery that many low organisms die only by
accident, and that if such accident be avoided, death does not fall on
them. Unicellular organisms (such as infusoria, many other protozoa
and low plants) multiply by simple division, the organism thus giving
rise to two new organisms; the parent so to speak loses itself in its
offspring without undergoing death. To criticisms of this mode of
presentment of the facts, Weismann, who has attracted most attention
to the view, replied as follows:—“In cultures of Infusoria, these
little animals continually multiply by division and no dead bodies are
found. The individual life is short, but it ends not in death but in
transformation to two new individuals.”
Max Verworn,[71] a physiologist of repute, objected that Weismann had
overlooked the occurrence within the organism of a process of partial
destruction, and that under certain conditions a complete organ of
the infusorian body (the nucleus) dies and is absorbed. Such death of
a part, however, is not followed by death of the whole, and as the
continuous destruction of some of the cells in our own bodies is not
regarded as our death, the criticism of the German physiologist cannot
be accepted.
It is not only the extremely short-lived microscopic organisms that
escape death. Some of the higher plants, which may attain to gigantic
size, encounter death only by accidents. There is nothing to be found
in the nature of their organisation which would seem to indicate that
death is the inevitable or even probable result of their constitutions.
The longevity of some trees has long been notorious, as these appear to
live for many centuries and to die only when they are overwhelmed by
the ravages of a storm or killed by human agency.
When the Canary Islands were discovered, in the beginning of the
fifteenth century, the early explorers were struck with the gigantic
size of a dragon tree which was venerated by the natives as their
tutelary deity. The tree stood in a Garden at Orotava in Teneriffe,
and even in these early days, its huge trunk contained a gigantic
hollow. The tree did not reward the worship of the natives, who
were annihilated by the Spaniards, and it survived them for nearly
four centuries. At the end of the eighteenth century it was seen
by Humboldt,[72] who found that the trunk was forty-five feet in
circumference, and who attributed to it a great age because dragon
trees grow extremely slowly. Early in the nineteenth century (1819) a
furious tempest swept over Orotava and with a gigantic crash nearly
a third of the crown of leaves and branches fell on the ground.
Notwithstanding this shock, the monster survived for fifty years.
Berthelot,[73] who visited it in 1839, described it as follows:—“A
dragon tree stood in front of my dwelling, grotesque in form, gigantic
in size, which a storm had smitten without overwhelming. Ten men would
have much ado to girdle its vast trunk, fifty feet in circumference at
the ground. The huge column had a deep cave within it, hollowed by the
ages; a rustic porch gave access to the interior, and the lofty dome,
although half had been destroyed by a storm, still bore an enormous
crown of branches.”
[Illustration: FIG. 15.—The Dragon-tree of the villa Orotava.]
The famous dragon-tree got more and more damaged, and was finally
overthrown by a storm in 1868. A few years after the catastrophe (in
1871) I myself saw the remains of the colossus, lying on the ground as
a huge grey mass like some antediluvian monster. No accurate estimate
of its age can be formed, but it must have lived several thousand years.
Trees have been known which were still older than the dragon-tree of
Teneriffe. One of the best known is the baobab of Cape Verd, described
by Adanson. “This remarkable tree was thirty feet in diameter when the
famous French naturalist measured and described it. Three centuries
earlier, some English sailors had cut an inscription on it, and
Adanson laid this bare by removing three hundred layers of wood. On
his observations Adanson based an estimate of 5,150 years as the age
of the tree.[74] The old cypresses of Mexico are thought to be still
older. A. de Candolle[75] concluded that the cypress of Montezuma was
2,000 years old when he saw it, and that the cypress at Oazaca was much
older than the tree described by Adanson. In California, trees of the
species _Sequoia gigantea_ are three thousand years old, and Sargent,
an American botanist, attributes to some of them an age of at least
five thousand years.
The question of the nature of individuality in the vegetable world
has been raised in connection with the longevity of trees. It has
been asked if a tree is to be regarded as a single individual or as
a colony of many plants like a branching polyp. It is a difficult
question, but only of secondary importance from the point of view of
this discussion. A. de Candolle,[76] having paid special attention to
the subject, came to the conclusion that trees do not die of old age,
that, in the real sense of the phrase, there is no natural end of their
existence. Many botanists agree with him. Naegeli[77] holds that a tree
several thousand years old dies only from external accidents.
It is plain that amongst the lower plants and the higher plants there
are cases where natural death does not exist. Theoretically, life would
have an unlimited duration, subject to the continuous replacement of
the substance of the organism in the normal metabolism. It must not be
inferred, however, that there is no such occurrence as natural death
amongst plants. There are numerous cases where death comes quite apart
from the agency of external forces. Even amongst closely related plants
there are some cases where natural death does not occur, and others
where it is normal. The lower fungi offer a good instance. Some of
these pass through a longer or shorter vegetative stage and then the
living mass breaks up into spores (_Myxomycetes_). The whole bulk of
matter is not transformed, but the remnant consists only of cuticular
secretions, not living cells. In other fungi, only some of the cells
transform to spores, the others dying naturally.
One stage of the life history of some lower plants is of short
duration. The prothalli of some cryptogams (_Marsiliaceæ_) live only a
few hours, just long enough for the appearance of the sexual organs.
When these are ripe the body of the prothallus and all its constituent
cells fall a prey to natural death. In such cases there is a “corpse,”
composed of dead cells and protoplasm. Even amongst the higher plants
there are instances of an extremely short duration of life. _Amaryllis
lutea_ passes through all the stages of its life-history in ten days,
the minimum time necessary for the sprouting of the leaves and flowers
and the production of the seeds, after which it dies naturally.[78] It
is interesting to find that in the same family there are other plants
notable for long duration of life. The Agave requires a century to
produce its flowers before death comes naturally.
Everyone is familiar with the so-called “annual” plants which live
only a few months, from the time when they sprout, until, after the
production of seed, death comes to them naturally. The life of annuals,
however, can be preserved for two or for several years. Rye is normally
an annual, but some varieties are able to live for two years and
produce two crops. The Cossacks of the Don have established this fact,
and have cultivated a biennial variety of rye for many years.[79]
Beetroot[80] is normally biennial, but has been changed to a plant
which lives for from three to five years. Such instances are by no
means unique.
Natural death can be postponed if the plant be prevented from seeding.
Professor Hugo de Vries has prolonged the life of the Oenotheras he
cultivates, by cutting the flowers before fertilisation. Under ordinary
conditions the stem dies after producing from forty to fifty flowers,
but, if cutting be practised, new flowers are produced until the winter
cold intervenes. By cutting the stem sufficiently early, the plants are
induced to develop new buds at the base, and these buds survive winter,
and resume growth in the following spring.” (Extract from a letter of
Prof. H. de Vries.)
The grass of lawns is usually mowed before it begins to flower, so as
to prevent the ripening of the seeds and the death of the plant. When
this is done, the grass remains continually green, and its life lasts
for several years.
The connection between the seeding of plants and their natural death
has been recognised for long, and is usually explained as being due to
the exhaustion of the plant.
As I am not a botanist, and was anxious to know the views of botanists
on natural death, I wrote to Prof. de Vries, as a universally accepted
authority. The distinguished botanist replied to me as follows. “Your
question is extremely difficult. I do not think that much is known as
to the exact cause of the death of annual plants, but it is customary
to attribute it to exhaustion.” All the botanists who have expressed
opinions on this matter appear to hold a similar view. Hildebrand,[81]
the author of a memoir on the duration of life in plants, stated this
view again and again. According to him “the life of annuals is usually
short because they are exhausted by their extensive production of seeds
(p. 116).” “Even amongst plants which produce seeds for several years,
there are some which are prematurely exhausted by fructification and
which die spontaneously” (p. 67). In the prothallus of many of the
higher cryptogams, the formation of a single embryo is followed by
natural death; as Goebel[82] points out, the embryo completely absorbs
the prothallus.
As plants generally obtain their food with ease, it is natural to ask
what is the cause of the exhaustion after seeding. When a plant which
cannot resist cold dies after it has produced its seeds in the end of
the summer, the event is natural enough. But how can we explain the
death of an annual plant which is growing in a rich soil, and which
seeds in the beginning of the summer, as being due to exhaustion long
before the winter cold. It frequently happens that after harvest new
shoots spring up from grains which have fallen. The soil which can
support this new vegetation cannot have been exhausted by the cereal
in question; and there has been enough warmth for the new crop. It
cannot be the external conditions which have caused the death of
the parent plant. The explanation of this apparent contradiction
has been sought in the constitution of the plant itself. Hildebrand
remarks that “certain species have a constitution which tends to early
fructification. As soon as the seeds have been set, the strength of the
plant is exhausted in the swelling of the grains, so that the plant
dies.” “Other species, on the contrary, are so constituted that they
vegetate for a long time, before fruiting, after which, however, they
also die. A third set of plants have such a constitution that “they
do not die after seeding, that they can seed often and live for many
years” (p. 113).
Being unable to indicate exactly the intrinsic mechanism of these
different “constitutions,” several botanists explain them by a kind of
teleological predestination. According to Hildebrand “the nutritive
processes of a plant have no other purpose than to make it capable of
reproduction; this final end, however, can be reached in different
modes and after different periods of time” (p. 132). Goebel sets
down similar views. “In heterosporous plants the whole course of the
development of prothalli is predetermined. The prothalli, so far as
we actually know, to use the phrase of theologians, are predestined;
their fate is determined once for all” (p. 403). M. Massart[83]
expresses the same kind of view, when he says that “sometimes cells
die because their work is finished, and they have no longer any reason
for existing.”
Such an interpretation of the facts is quite opposed to determinism,
and makes the problem of natural death in the plant world more
difficult but more interesting.
The modern scientific conception of the universe excludes the idea
of predestination. The relations between fructification and natural
death must be regulated by the law of selection, according to which no
organism survives if its reproduction is impossible. It occasionally
happens that children are born without organs which are indispensable
to life. Such monsters of different kinds being non-viable, cannot be
said to be predestined to death, as they die because of defects in
their structure. Others are born with all that is necessary for life,
and survive for that reason, not because they are predestined to life.
So also species of plants which develop incompletely and which die
before they have produced spores or seeds, cannot survive; whilst those
which die after having given birth to the next generation survive in
their descendants. However quickly death follow the production of seed,
the species will survive equally well. The cause of the natural death
of plants must be sought, therefore, not in predestination, but in the
mechanism of the organic processes.
Nothing seems more probable than that a plant should die when all its
organic forces have been exhausted. It would be interesting, however,
to ascertain the mechanism of that exhaustion, and this especially
because it is often very difficult to imagine a cause for it. Many
plants exist which produce several generations each season, in the same
soil, without exhausting it. In perennial plants, some parts, such
as the flowers, die periodically, although the plant itself is not
exhausted. Everyone has seen that in geraniums some of the flowers
wither whilst others are blooming, the process going on throughout the
season. We can scarcely attribute such a natural death of the flowers
to any exhaustion of the plant which continues to produce new flowers.
The fairly frequent prolongation of the life of plants is also
out of harmony with the theory of natural death as the result of
exhaustion. It sometimes happens that male plants produce female
flowers abnormally; cases of this kind have been observed in willows,
stinging-nettles, hops, and especially in maize.[84] Here we have
to deal with a kind of monstrosity, differing, however, from the
non-viable monsters of the human race, in the respect that the
production of female flowers on the male branches results in the
prolongation of their lives. Generally the male branches die a natural
death as soon as the pollen has been shed, and therefore some time
before the death of the female flowers. If, however, a male branch
bears a female flower which becomes fertilised, then the life of the
branch is prolonged until the seeds ripen. If the natural death of the
male flowers is the result of exhaustion due to the development of the
pollen, how can we reconcile this with the prolongation of life in a
case where the male branch has also female flowers to nourish and seeds
to mature?
It is quite clear that natural death, in such cases, is the result of a
mechanism more complex than simple exhaustion.
Prof. de Vries has already noted that the duration of life in plants
depends on their vital processes. That view implies that there are some
qualities inherent in its organisation which can prolong or shorten
the life of a plant, and it is here that we ought to find the key
to the problem of natural death in the vegetable world. However, to
gain exact knowledge of such factors, it would be necessary to have
information on many points in plant physiology which unfortunately are
very imperfectly known. In this respect, the vital conditions of the
simplest plants, such as yeasts and bacteria, have been investigated
much more fully. It is true that such low organisms reproduce freely
either by division or by budding, so that they are amongst the
organisms in which natural death is not inevitable. None the less, in
their lives phenomena occasionally present themselves which can be
interpreted as cases of natural death.
At a time when it was still unknown that all fermentation was due
to the action of microscopic plants, it had been observed that, in
certain conditions, fermentation ceased much more quickly than in
other conditions. For instance, when sugar is being transformed to
lactic acid, it is useful to add chalk, as otherwise the fermentation
stops before the greater part of the sugar has been acted upon. When,
in 1857, Pasteur made his great discovery of the lactic acid microbe,
he showed that that little organism, although it could produce lactic
acid, was interfered with by an excess of the acid. To secure complete
fermentation, it was necessary to neutralise the acid by the addition
of chalk.
When the action of lactic acid is continued too long, it not only
arrests the process of fermentation but definitely kills the microbe.
It is for that reason that it has been found difficult to preserve the
lactic acid ferment for a long time in a living condition. Amongst the
ferments which have been isolated from Egyptian ‘leben’ by MM. Rist and
Khoury[85] there is one which is extremely delicate.
When it is inoculated deep in a nutritive medium, it dies in a few
days, death, without doubt, being due to the lactic acid produced by
the microbe from the sugar and not neutralised. As this transformation
of sugar into lactic acid is a fundamental property of the microbe,
depending on its constitution, the arrest of the fermentation and the
death of the ferment in these definite conditions can be interpreted
only as natural death due to auto-intoxication, that is to say to
poisoning by a product of the physiological activity of the microbe
itself. As death takes place at a time when the medium still contains
enough sugar for the nutrition of the microbe, it is certain that
it cannot be the result of exhaustion. This case of the lactic acid
ferment is not unique. The microbe which produces butyric acid is
also interfered with by the acid it secretes. M. G. Bertrand, who has
examined carefully the microbe which produces fermentation in sorbose
(sugar extracted from fruit of the service-tree) (_Sorbus domestica_)
has informed me that this fermentation, too, ceases under the influence
of the secretions of the microbes, and that the microbes undergo
natural death at a time when the medium is far from exhausted of the
nutritive material. The yeast which produces alcohol is also interfered
with by an excess of alcohol, and as soon as a certain limit of
alcoholic strength has been reached, fermentation stops. When the yeast
is grown in media rich in nitrogen and poor in sugar, the plant takes
the nitrogenous material and produces salts of ammonia. These alkalies
damage the yeast and cause its death by auto-intoxication.[86]
In the examples that I have given, natural death was a result of
the activity of the microbes, and was in correlation with their
organisation. Such death can be avoided by changing the external
conditions, and, if the acids or alkalies produced by these bacteria
are neutralised, the bacteria survive. The facts are in harmony with
those that I described in the case of the higher plants. By preventing
the ripening of seed, the life of many annual plants may be preserved
and the plants changed to biennials or perennials. In such cases death,
although the result of the constitution of the plant, may be postponed.
We may ask then if the natural death of higher plants, usually
attributed to exhaustion, cannot be explained more simply as the
result of poisons produced in their metabolism. Many plants produce
poisons which are fatal to animals and man. May they not also produce
substances fatal to themselves? There is nothing improbable in the
supposition that some of the poisons may develop when the seeds are
ripening. By preventing the latter process, the ripening of the whole
organism may also be prevented. Such a theory would explain the many
cases of natural death which occur whilst the cell is far from having
reached exhaustion. The equally numerous cases of partial death, such
as that of flowers, whilst the same stem is still producing other
flowers (_e.g._ geraniums) would be explained by a local action of the
poisons not strong enough to kill the whole plant.
I must insist that this theory, that natural death of the higher
plants, is the result of auto-intoxication, is a mere hypothesis
which future investigations may disprove. If, however, it comes to be
confirmed, it would explain the coincidence of death and fructification
more simply than the hypothesis of predestination.
The higher plants may be subjects of auto-intoxication in the same
fashion as bacteria and yeasts. If these poisons were produced before
the ripening of the seeds, the plants would remain sterile, leaving
no descendants, so that the race would become extinct. The production
of poisons at the time of fructification would not interfere with the
succession of generations, and the race would be preserved. As the
poisoning is not necessary, it is easy to understand why many plants
survive seeding and escape natural death. The Dragon-tree, baobab, and
the cedars, which I spoke of earlier, would be examples of such escape.
Although the existence of auto-intoxication in the higher plants is
still only a hypothesis, the natural death of bacteria and yeasts by
poisons which they themselves produce is an ascertained fact.
In the plant world, therefore, there are examples of natural death
(bacteria and yeasts) due to auto-intoxication, and there are other
cases where high or low plants escape natural death.
II
NATURAL DEATH IN THE ANIMAL WORLD
Different origins of natural death in animals—Examples
of natural death associated with violent acts—Examples
of natural death in animals without digestive
organs—Natural death in the two sexes—Hypothesis as to
the cause of natural death in animals
The cases of natural death amongst animals differ from those found in
the vegetable world by their greater variety and complexity. As M.
Massart has shown for plants, so also natural death must have become
established independently in different groups of animals. In some
cases, the characters presented are strange and almost paradoxical.
It is usual to contrast natural death with violent death on account of
the difference between the two. None the less, natural death may occur
in the animal kingdom, that is to say death resulting directly from the
constitution, and yet in intimate association with violent acts. I will
give some examples.
Small, helmet-shaped organisms, transparent and graceful, are common on
the surface of the sea. These have been described by zoologists under
the name _Pilidium_. The organisation is simple. The body wall is a
delicate pellicle, through which, on the lower surface, a mouth leads
into a capacious stomach. Continual movements of waving cilia direct
small particles of food through the mouth to the digestive stomach.
As there are no organs of reproduction, it was assumed that these
creatures were not adults, but floating larvæ of some marine animal,
and, after a good deal of trouble, it was found that the Pilidia were
the young stages of ribbon-shaped worms of the group of Nemertines.
At a definite stage in the life-history, a fœtus begins to develop
round about the stomach of the Pilidium, and eventually completely
encloses it and detaches it by violent muscular contractions. The end
of the story is that the fœtus abandons the body of the Pilidium
carrying off with it the stomach, an organ necessary to the maintenance
of life. The remnant of the Pilidium swims about in the sea-water, but
soon dies as the result of the mortal wound caused by the removal of
the digestive organs.
The act by which the Nemertine separates from its mother is violent,
and yet the death of the Pilidium must be regarded as natural. It is
the result of agencies within the body and not, as in most cases of
accidental death, of violence from without.
The group of Nematode worms contains many common intestinal parasites
of man, such as _Ascaris_, _Trichina_, _Trichocephalus_, _Oxyuris_,
&c., but also others that live free in soil or water or in such fluids
as vinegar. They are protected by a strong cuticle, and some of them
are viviparous, that is to say, instead of laying eggs they give
birth to young worms already well grown and capable of independent
activity. Amongst the human Nematode parasites, the _Trichinæ_ give
birth to swarms of small larvæ which easily escape from the body of
the mother by the female generative aperture. In the case of some
free-living Nematodes, however, the female aperture is too small to
give passage to the rather stout larvæ. More than forty years ago, when
I was investigating the life-history[87] of one of these Nematodes
(_Diplogaster tridentatus_) I was struck by the fact that the larvæ
could leave the body of the mother only by violence and after they had
devoured most of its substance. These larvæ develop from eggs produced
within the maternal body. As the external reproductive aperture of
the female is minute, the larvæ cannot escape through it, but wander
amongst the tissues tearing and absorbing them. The mother soon dies,
and although her death is violent, it must be included in the category
of natural death.
From the teleological point of view it might be said that Pilidium
and Diplogaster cease to live because they have fulfilled their
function of giving rise to a Nemertine or young Nematodes. Their
natural death would thus be predestined. There is no ground for such
an interpretation. On the other hand, it is certain that this death,
coming after the birth of the new generation, is in no way against the
preservation of the species in which the extraordinary natural death
by violence occurs. If the female orifice of Diplogaster were slightly
larger, the larvæ would emerge without difficulty and without causing
the death of the mother which none the less would have fulfilled her
purpose.
All the cases of natural death amongst animals are not so brutal as
those of the Pilidium and the Nemertine worms. In many instances the
death is peaceful. As very frequently it is difficult to establish
definitely that the death is natural, I shall select clear cases.
Animals are occasionally found which are devoid of some organ necessary
for prolonged life. The absence of a digestive tract in an animal that
lives in an environment rich in dissolved nutritive material (as for
instance tapeworms living in the intestinal tract) is not surprising.
But when creatures of the sea or of fresh water have no digestive
tract, their life can be maintained only at the expense of nutritive
material stored within them during embryonic life. The death which
comes eventually is truly natural. The best cases, that is to say those
which can be studied most completely, of such natural death occur
amongst the Rotifera. These are minute creatures of fresh or sea water,
at one time confused with the Infusoria, but possessed of a much more
complex organisation. They have a well-developed digestive tube, organs
of excretion, nervous system, and organs of sense. The animals are
diœcious; in each species both males and females exist. Whilst the
females have the complete structure of the species, the males are much
reduced, and are devoid of a digestive canal. The cuticle is fairly
stout, and they are unable to absorb dissolved nutriment through it; as
they have no organs of digestion, their life must be short.
To study in detail the life and death of these creatures, I selected a
species sent to me by M. Haffkine. So far as I can judge, the species
in question is a hitherto unknown member of the genus _Pleurotrocha_,
and I propose for it the name _Pleurotrocha haffkini_. This rotifer is
convenient to study as it thrives in vessels containing fresh-water to
which some bread-crumb has been added (in the proportion of a gram of
bread to 500 grams of water).
The sexes of the little rotifer can be distinguished from the earliest
age, for eggs that are to become females are much larger than those
from which males develop. It is easy to isolate the male eggs and to
follow the life-history up to the moment of natural death. The whole
course of life from the laying of the egg until death lasts only about
three days, and is probably the shortest duration of life in the animal
kingdom. Although some Ephemeridæ live only a few hours in the adult
state, their total life-cycle is much longer than that of the rotifers,
as the larval stages last for months or even for years.
[Illustration: FIG. 16.—Male _Pleurotrocha haffkini_.]
The little males (Fig. 16) begin to swim soon after hatching, the
wheel-apparatus and the musculature being vigorous. They seek out
the females, as their reproductive organs are mature almost at the
moment of hatching. The transparent body, which is devoid of digestive
apparatus, swarms with mobile spermatozoa. As soon as the male has
seized a female, he discharges the contents of his body. It might be
supposed that such an evacuation would cause a violent perturbation of
the system leading to the death of the organism. There is no question
of this however. The males are able to live for twenty-four hours after
having accomplished their function, and the period represents a third
of their total duration of life. Moreover, I have isolated males from
females without any prolongation of their lives. In one experiment, I
isolated two males and placed a third in company with two females. It
was the third specimen that lived longest.
The natural death of the males is foreshadowed by a weakening of the
movements; although the muscles and cilia remain mobile, the whole
animal moves only spasmodically; sometimes the muscles of the head
contract, sometimes those of the tail, but no locomotion occurs.
Occasionally there is a violent effort of ciliary motion as if the
attempt were being made to overcome the immobility of the body. Such
a condition lasts for several hours and is followed by death. The
spermatozoa inside the body retain activity last of all.
Towards the crisis, bacteria, which abound in the medium occupied by
the rotifers, begin to attack the males. Some cluster round the head,
others round the tail, although none of them can effect entrance to
the body. The death of the males cannot be attributed to microbial
infection, but comes from some intrinsic cause.
Is it inanition that is the cause of death? I do not think so, because
up to the time of death the tissues appear to be unmodified. In the
case of the females I have sometimes seen phenomena of inanition. In
old and exhausted cultures the starved females become thin, flattened
and quite transparent, and the tissues lose their granular appearance.
No such changes are visible in the dying males, the tissues of which,
on the contrary, retain a normal aspect.
The most probable explanation is that death comes from poisoning by the
secretions of the tissues themselves. The large size of the organs of
excretion indicates that in the course of metabolism waste matter is
produced some of which is got rid of. If, after a time, the secretions
are insufficiently eliminated, the tissues must be poisoned. As death
is preceded by a spasm of uncoordinated movement, it appears as if the
fatal intoxication of the males affected the nervous system first. The
vibrating cilia and the muscles are attacked later.
There can be no doubt but that the death of these male rotifers is
natural in the fullest sense. The females, however, although they are
provided with complete digestive organs, do not escape a similar fate.
Their life is longer and more complex than that of the males, and so
is subject to many more chances. The females therefore may come to die
from starvation or from other external, accidental causes. But, if they
are kept in favourable conditions, they may live for about fifteen
days, towards the end of which they die naturally, exhibiting the
symptoms that I have described in the case of the males (Fig. 17).
[Illustration: FIG. 17.—Female _Pleurtrocha haffkini_, which has died
a natural death.]
Rotifers are not the only animals which undergo natural death in a
fashion quite unlike the violent end of Pilidium and Diplogaster. There
are other cases amongst invertebrates, but I shall limit myself to
describing one that is well ascertained.
More than fifty years ago, Dana, the American naturalist, discovered a
pelagic marine creature with characters so curious that he gave to it
the name _Monstrilla_. It is a little crustacean akin to the _Cyclops_
of lakes. But although the latter is endowed with the organs necessary
to capture and digest food, _Monstrilla_ has neither organs of
prehension nor a digestive canal. It is a highly muscular animal with
organs of sense and reproduction and a nervous system; but it is devoid
of apparatus for prolonging life by nutrition. _Monstrilla_ therefore
is a creature doomed to natural death.
[Illustration: FIG. 18.—_Monstrilla._ (After M. Malaquin.)]
The detailed observations of M. Malaquin[88] have supplied full
information regarding this strange life-history. _Monstrilla_ passes
a portion of its life as a parasite on Annelid worms. In that stage
it accumulates the necessary material for the growth of the sexual
products (ova and spermatozoa) and for free life in the sea whilst the
young are developing. It is not only the males which have no digestive
apparatus. The females also lack it, which is the more surprising as
they carry about the eggs attached to the body (as is done by many
other Crustacea, such as crayfish and lobsters) until the young are
ready to hatch (Fig. 18). M. Malaquin thinks that the Monstrillas die
of starvation.
“As they are without a digestive tube or organs of prehension or
mastication,” M. Malaquin says (p. 192), “the Monstrillas, which have
no means of nutrition, are doomed to death from inanition after a short
pelagic life. This is a logical inference from their structure.”
In support of his view, M. Malaquin states that before death the
tissues and organs show plain signs of degeneration.
“The eyes first show traces of degeneration. The pigment spreads and
disappears little by little and then the visual elements fade out.”
“Finally, individuals, usually females, show complete degeneration.
A female taken in a fine-meshed net showed no trace of organs in the
head; the eyes, the brain and the intestinal tract had disappeared
almost completely. The antennæ were reduced to stumps consisting of the
lowest joint and a portion of the second. These were clear indications
of the senility that precedes death” (p. 194).
Such evidence not only supports the hypothesis that the natural
death of Monstrilla is due to inanition, but is opposed to a similar
interpretation being applied to the case of male rotifers, in which
death is not preceded by wasting of the organs. The death of some
insects, which comes rapidly after the adult stage has been reached,
cannot readily be attributed to starvation. In the strange butterflies
known as psychids (_Solenobia_) some of the females lay eggs without
having been fertilised,[89] and their life in the adult condition lasts
only a day. On the other hand, other females of the same butterfly
are fertilised before laying their eggs and in this case survive for
more than a week although they take no food. The rapid death of the
first-mentioned set cannot be attributed to inanition.
In some Ephemeridæ, which supply good cases of natural death, the end
comes after a few hours of adult life without any sign of degeneration
of the organs. As in others (_Chloë_), life lasts for several days
without food having been taken, it is clear that inanition is not
the cause of the swift arrival of death in the first set. It is much
more probable that the natural death is due to an auto-intoxication
which takes effect at different intervals of time in different
circumstances.[90]
In the higher animals such as vertebrates the conditions are less
favourable than in the case of insects for the investigation of the
causes of natural death. Vertebrates have always well-developed organs
of digestion and so live a relatively longer time and encounter a
greater number of chances of accident, with the result that in most
cases death comes from external accidental causes. Vertebrates usually
perish from hunger or cold, or are devoured by their enemies or killed
by the attacks of parasites or diseases. There remains only the human
race amongst the more highly developed animals, in which to study
the onset of natural death. And in the human race cases which may be
designated as natural are extremely rare.
III
NATURAL DEATH AMONGST HUMAN BEINGS
Natural death in the aged—Analogy of natural death and
sleep—Theories of sleep—_Ponogenes_—The instinct
of sleep—The instinct of natural death—Replies to
critics—Agreeable sensation at the approach of death
The death of old people, which has often been described as natural
death, is in most cases due to infectious diseases, particularly
pneumonia (which is extremely dangerous) or to attacks of apoplexy.
True natural death must be very rare in the human race. Demange[91]
has described it as follows:—“Arrived at extreme old age, and still
preserving the last flickers of an expiring intelligence, the old man
feels weakness gaining on him from day to day. His limbs refuse to obey
his will, the skin becomes insensitive, dry, and cold; the extremities
lose their warmth; the face is thin; the eyes hollow and the sight
weak; speech dies out on his lips which remain open; life quits the
old man from the circumference towards the centre; breathing grows
laboured, and at last the heart stops beating. The old man passes away
quietly, seeming to fall asleep for the last time.” Such is the course
of what properly speaking is natural death.
The natural death of human beings cannot be regarded as due to
exhaustion from reproduction or from inanition, as in the case
of _Monstrilla_. It is much more likely that it is due to an
auto-intoxication of the organism. The close analogy between natural
death and sleep supports this view, as it is very probable that sleep
is due to poisoning by the products of organic activity.
It is more than fifty years since sleep was explained as the result
of auto-intoxication. Obersteiner, Binz, Preyer, and Errera are among
the competent men of science who have taken this view. The first two
attributed sleep to an accumulation in the brain of the products of
exhaustion which are carried away by the blood during repose. The
attempt has been made even to discover the nature of these narcotic
substances. Some investigators think that an acid, produced during
the activity of the organs, is stored up in quantities that cannot be
tolerated. During sleep, the organism gets rid of this excess of acid.
Preyer[92] tried to put the problem upon a more exact basis by the
theory that the activity of all the organs gives rise to substances
which he called _ponogenes_ and which he regarded as producing the
sensation of fatigue. According to him these substances accumulate
during the waking hours, and are destroyed by oxidation during sleep.
Preyer thinks that lactic acid is the most important of the ponogenes,
and lays stress on its narcotic effect. If his theory were correct,
there would be a remarkable analogy between the auto-intoxication by
lactic acid in the cases of man and animals, and the case of bacteria
which produce the same acid and the fermenting activity of which is
arrested as the acid accumulates. Just as sleep may be transformed
to natural death, so also the arrest of lactic fermentation may be
followed by the death of the bacteria which form the acid.
So far, however, there has been no confirmation of Preyer’s theory.
Errera[93] has brought forward against it another theory according
to which the cause of sleep is not acid products, but certain
alkaline substances described by M. Armand Gautier under the name of
_leucomaines_. Gautier laid down that these substances act on the
nervous centres and produce fatigue and sleepiness. According to Errera
they might very well be the cause of sleep, as that comes on at a
time when there is the greatest accumulation of these leucomaines in
the body. He thinks that their action in producing sleep is a direct
intoxication of the nerve centres. During sleep they are removed, and
the disturbance which was produced in the organism is arrested.
If it were possible to accept Errera’s theory, a kind of analogy could
be established between sleep and natural death on the one hand, and
the arrest of development and death of yeast grown in nitrogenous
media on the other hand, because in the latter case the poisoning is
produced by an alkaline salt of ammonia. It must be confessed, however,
that the actual state of our knowledge does not allow of a definite
view of the real mechanism of the sleep-producing intoxication. Our
ideas regarding leucomaines in general are still incomplete, and,
recently, one of them, _adrenaline_, the product of the supra-renal
capsules, has been investigated. Adrenaline is an alkaloid[94] which is
produced in the supra-renal bodies and is discharged into the blood.
It has the power of contracting arteries strongly, and has been used
to control blood-pressure. When it is given in large quantities or
in frequent doses, it acts as a true poison, whilst, in small doses,
it produces anæmia of the organs and has a special influence on the
nervous centres. Dr. Zeigan[95] has shown that a milligramme of
adrenaline, mixed with five grammes of normal salt solution injected
into the brain of cats, produces a soporific action. “About a minute
after the injection, the animal appears to be plunged into deep sleep
which lasts from 30 to 50 minutes. During this time, the sensitiveness
of the animal has completely ceased throughout the body, and for some
time after that it is much decreased. When they awake the animals
seem to have been drunk with sleep for some time.” Sleep is generally
associated with anæmia of the brain, and as adrenaline can actually
produce such anæmia, it might be supposed that this narcotic substance
is the most important of the organic products which give rise to sleep.
Against this hypothesis, however, some weight must be given to recent
investigations on fatigue and its causes.
Each stage in the advance of knowledge has had its influence on
the study of the interesting and complex problem of sleep. When it
was thought that alkaloids (ptomaines) were of great importance in
infectious diseases, it was attempted to explain sleep as due to the
action of similar bodies. Now, when we believe that in such diseases
the chief part is played by poisons of extremely complex chemical
composition, the attempt is made to explain fatigue and sleep by
similar bodies.
Weichardt[96] has recently made the best known investigations in this
direction. This young man maintains with ardour the view that during
the activity of organs there is an accumulation of special materials
which are neither organic acids nor leucomaines, but which are much
more like the toxic products of pathogenic bacteria.
Weichardt made animals in his laboratory go through fatiguing
movements for hours and then killed them. The extract from muscles of
such animals had a powerful toxic effect when it was injected into
normal animals, producing lassitude and sometimes death within 20 to
40 hours. As all attempts to determine the exact chemical nature of
this fatigue-producing substance were baffled, it is impossible to get
an exact account of it. Amongst its properties there is one of great
interest. When it has passed into the circulation of normal animals in
quantities insufficient to produce death, it excites the formation of
an anti-toxin in the same way as a poison of diphtheria stimulates the
production of a diphtheria anti-toxin.
When Weichardt injected into animals a mixture of the poison which
produces fatigue with small doses of the serum antidote, no results
followed. The neutralising effect of the antidote was apparent
even when it was introduced by the mouth. Towards the end of his
investigations, Weichardt supposed that it would be possible to obtain
a material that would prevent fatigue.
Although it is still impossible to specify exactly the nature of the
substances which accumulate during the activity of organs and which
produce fatigue and sleep, it is becoming more and more probable that
such substances exist, and that sleep is really an auto-intoxication
of the organism. So far, such a theory has not been shaken by any
argument. Recently M. E. Claparède,[97] a psychologist of Geneva,
has argued against the current theory of sleep. He thinks that it
is contradicted by the fact that new-born infants sleep a great
deal, whilst very old people sleep very little. This fact, however,
can readily be explained by the greater sensibility of the nerve
centres of infants, as shown with regard to many harmful agencies. The
other objections of Claparède, such as the fact that sleepiness is
induced by exercise in the open air, or that excess of sleep itself
produces sleepiness, are not really incompatible with the theory of
auto-intoxication. They are facts of secondary importance probably
depending on some complication which the present state of our knowledge
makes it difficult to indicate exactly. The insomnia of neurasthenia,
which Claparède brings forward as another objection, can readily be
explained as due to hyperæsthesia of the nervous tissues which lose
part of their sensitiveness to poisons.
On the other hand, there are many well established facts in agreement
with the theory of auto-intoxication. Leaving out of the question
sleep induced by narcotics, I may mention in this connection the
so-called “sleeping sickness.” It has been proved that this disease
is caused by a microscopic parasite, the _Trypanosoma gambiense_ of
Dutton, which develops in the blood and spreads to the liquid of the
membranes surrounding the central nervous system. One of the most
typical symptoms of the advanced stages of this disease is continual
drowsiness. “The drowsiness increases progressively, and the habitual
attitude becomes characteristic; the head is bent on the breast; the
eyelids are closed; in earlier stages the invalid can be aroused
easily, but, after a time, incurable attacks of sleep overcome the
patient in all circumstances, but especially after meals. These
fits of sleepiness become longer and deeper, until they reach a
comatose condition from which it is almost impossible to arouse the
patient.”[98] The total result of medical knowledge of this disease
is that it is impossible to doubt that the sleepiness is due to
intoxication produced by the poison of the trypanosome.
Claparède has opposed what he calls an “instinctive” theory to
the toxic theory of sleep. According to this theory, sleep is the
manifestation of an instinct “the object of which is to arrest
activity; we do not sleep because we are intoxicated or exhausted, but
to prevent ourselves from falling into such a condition.” However, in
order to bring this narcotic instinct into play, certain conditions
are necessary, one of which certainly would be the intoxication of
the nerve centres. M. Claparède supposes that sleep is an active
phenomenon, induced when waste matter begins to accumulate in the
organism. “To bring about sleep, the nerve centres must be influenced
by waste matter, and this influence can readily be regarded as a kind
of intoxication.”
Hunger is an instinctive sensation as much as sleepiness, but it does
not appear until our tissues are in a condition of exhaustion, the
exact nature of which cannot as yet be indicated. There is no real
contradiction between the toxic and instinctive theories of sleep. The
two theories represent different sides of a special condition of the
organism.
The analogy between sleep and natural death is in favour of the
supposition that the latter, also, is due to an intoxication much more
profound and serious than that which results in sleep. Therefore, as
natural death in human beings has been studied only very superficially,
it is impossible to do more than frame theories regarding it.
It would be natural if, just as in sleep there is an instinctive
desire for rest, so also the natural death of man were preceded by an
instinctive wish for it. As I have already discussed this subject in
the “Nature of Man” (chap. xi) I need not deal with it at length here.
I should like, however, to add some information which I have recently
obtained.
The most striking fact in favour of the existence of the instinct for
natural death in man appears to me to have been related by Tokarsky
in regard to an old woman. While Tokarsky was alive I asked one of
his friends to obtain for me further details of this very interesting
case. Unfortunately Tokarsky could add nothing to what he had already
published in his article. I think that I have discovered the source of
his information. In his famous book on the _Physiology of Taste_[99]
Brillat-Savarin relates as follows:—“A great-aunt of mine died at
the age of 93. Although she had been confined to bed for some time
her faculties were still well preserved, and the only evidence of her
condition was the decrease in appetite and weakening of her voice.
She had always been very friendly to me, and once when I was at her
bedside, ready to tend her affectionately, although that did not
hinder me from seeing her with the philosophical eye that I always
turned on everything about me, ‘Is it you, my nephew?’ she said in
her feeble voice. ‘Yes, Aunt, I am here at your service, and I think
you will do very well to take a drop of this good old wine.’ ‘Give it
me, my dear; I can always take a little wine.’ I made ready at once,
and gently supporting her, gave her half a glass of my best wine. She
brightened up at once, and turning on me her eyes which used to be so
beautiful, said: ‘Thank you very much for this last kindness; if you
ever reach my age you will find that one wants to die just as one wants
to sleep.’ These were her last words, and in half an hour she fell into
her last sleep.” The details make it certain that this was a case of
the instinct of natural death. The instinct showed itself at an age
not very great in the case of a woman who had preserved her mental
faculties. Generally, however, it seems not to appear till much later,
for old men usually exhibit a keen wish to live.
It is a well-known saying that the longer a man has lived the more
he wishes to live. Charles Renouvier,[100] a French philosopher who
died a few years ago, has left a definite proof of the truth of the
saying. When he was eighty-eight years old, and knew that he was
dying, he recorded his impressions in his last days. Let me quote from
what he wrote four days before his death. “I have no illusions about
my condition; I know quite well that I am going to die, perhaps in a
week, perhaps in a fortnight. And I have still so much to say on my
subject.” “At my age I have no longer the right to hope: my days are
numbered, and perhaps my hours. I must resign myself.” “I do not die
without regrets. I regret that I cannot foresee in any way the fate
of my views.” “And I am leaving the world before I have said my last
word. A man always dies before he has finished his work, and that
is the saddest of the sorrows of life.” “But that is not the whole
trouble, when a man is old, very old, and accustomed to life, it is
very difficult to die. I think that young men accept the idea of dying
more easily, perhaps more willingly than old men. When one is more
than eighty years old, one is cowardly and shrinks from death. And
when one knows and can no longer doubt that death is coming near, deep
bitterness falls on the soul.” “I have faced the question from all
sides in the last few days; I turn the one idea over in my mind; I
_know_ that I am going to die, but I cannot _persuade_ myself that I
am going to die. It is not the philosopher in me that protests. The
philosopher does not fear death; it is the _old man_. The old man has
not the courage to submit, and yet I have to submit to the inevitable.”
I know a lady, a hundred and two years old, who is so oppressed by
the idea of death, that those about her have to conceal from her the
death of any of her acquaintances. Mde. Robineau, however, when between
one hundred and four and one hundred and five years old, became quite
indifferent to the close approach of her own death. She often expressed
a wish for it, thinking herself useless in the world.
M. Yves Delage[101] in an analysis of my “Nature of Man” doubted the
existence of an instinct for death. “Animals,” said he, “cannot have
the instinct for death, because they do not know of death. In their
case, we must consider that what happens is an apathy tending to the
abolition of the sense of self-preservation. In man, the knowledge
of death implies that the indifference to its approach cannot be an
instinct.” “There may be developed, at the end of life, a special state
of mind which accepts death with indifference or with pleasure, but
such a state cannot be designated as an instinct.” M. Delage, however,
does not suggest what the state of mind in question is to be called.
As the aunt of Brillat-Savarin compared her sensations just before
death with the desire to sleep, and as this desire is an instinctive
manifestation, I think that the cheerful acquiescence in death,
exhibited by extremely old people, is also a kind of instinct. However,
the important matter is that the sentiment exists, and not what we are
to call it. M. Delage is far from denying its existence.
Dr. Cancalon,[102] another of my critics, cannot admit the existence
of an instinct of death, “because of the theory of evolution. Of what
good would it have been, as M. Metchnikoff tells us that natural death
is very rare; how could it have been transmitted, as it comes into
existence long after the age of reproduction, and how could it have
aided the survival of the species? If its existence were proved as
the result of biological evolution, it would be a contradiction of
adaptation and an argument in favour of final causes.” I cannot agree
in any way with these opinions. In the first place, it is well known
that men and animals have many harmful instincts that do not tend
to the survival of the species. I need recall only the disharmonic
instincts which I described in the “Nature of Man,” such as the
anomalies of the sexual instinct, the instinct which drives parents to
devour their young or which attracts insects to flames. The instinct
of natural death is far from being harmful, and may even have many
advantages. If men were convinced that the end of life were natural
death accompanied by a special instinct like that of the need for
sleep, one of the greatest sources of pessimism would disappear. Now
pessimism is the cause of the voluntary death of a certain number of
people and of many others refraining from reproduction. The instinct
of natural death would contribute to the maintenance of the life of
the individual and of the species. On the other hand, there is no
difficulty in admitting the existence of instincts hostile to the
preservation of the species, especially in the case of man, in whom
individualism has reached its highest development. As man is the only
animal with a definite notion of death, there is nothing extraordinary
if it is in man that the instinctive wish for death develops. M.
Cancalon denies the possibility that death can be pleasant, as it is
the arrest of the physiological functions; but as sleep and syncope
are often preceded by very pleasant sensations, why may not this also
happen in natural death? Several facts prove it beyond dispute. It is
even probable that the approach of natural death is one of the most
pleasant sensations that can exist.
It is indubitable that in a large number of cases of death, the
cessation of life is associated with very painful sensations. One has
only to see the horror shown in the faces o£ many dying people to be
convinced of this, but there are diseases and serious accidents in
which the approach of death does not arouse sorrowful sensations. I
myself, in a crisis of intermittent fever, in which the temperature
descended in a very short time from about 106° Fahr. to below normal,
experienced a feeling of extraordinary weakness, certainly like that
at the approach of death. This sensation was much more pleasant than
painful. In two cases of serious morphia poisoning, my sensations were
more agreeable; I felt a pleasant weakness, associated with a sensation
of lightness of the body, as if I were floating in the air.
Those who have noted the sensations of persons rescued from death have
related similar facts. Prof. Heim, of Zurich, has described a fall
in the mountains which nearly killed him, as well as several similar
accidents to Alpine tourists. In all these cases he states that there
was a sensation of pleasure.[103] Dr. Sollier has told of a young woman
addicted to morphia, who had been convinced that she was at the point
of death. On recovering from a most serious attack of syncope, from
which she was restored only by giving another dose of morphia, she
cried: “I seem to come from far away; how happy I was!” Another of
Dr. Sollier’s patients, a lady who had an attack of peritonitis from
which she expected to die, felt herself “suffused with a feeling of
well-being, or rather the absence of all pain.” In a third Case of Dr.
Sollier, a young woman suffering from puerperal fever, feeling herself
at the point of death, had a similar sensation “of physical well-being
and of detachment from everything.”[104]
As a sensation of happiness occurs even in cases of pathological death,
it is much more likely to occur in natural death. If natural death be
preceded by the loss of the instinct of life and by the acquisition of
a new instinct, it would be the best possible end compatible with the
real organisation of human nature.
I do not pretend to give the reader a finished study on natural death.
This chapter of Thanatology, the science of death, only opens the
subject; but it is already apparent that study of the circumstances of
natural death in plants, in the animal world, and in human beings, may
give facts of the highest interest to science and humanity.