THE CONTRIBUTIONS OF BIOLOGY AND PHYSIOLOGY
Weismann’s immortality of the germ plasm and his denial of the
inheritance of acquired qualities--The truth and limitations
of his views--The theories of Hering and Simon--Metchnikoff’s
conception of the disharmonies in man, of the rôle of intestinal
flora and their products, of euthanasia, and of the means
and effects of prolonging life--C. S. Minot’s conception of
the progressive arrest of life from birth on as measured by
declining rate of growth and his neglect to consider the
dynamic elements--C. M. Child’s studies of rejuvenation in
lower and higher forms of life in the light of the problems
of senescence--J. Loeb’s studies of the effects of lower
temperatures, of toxins, and ferments--The preservation of
cells of somatic tissues potentially immortal under artificial
conditions--Account of the studies of Carrel, Pozzi, and
others--Investigations upon the effects on sex qualities and
age of the extracts and transplantations of glands, from Claude
Bernard--Investigations of Eugene Steinach on the interchange of
sex qualities and rejuvenation by glandular operations in animals
and man--G. F. Lydston’s work--Serge Voronoff’s experiments
and his exposition of the achievements and hopes of glandular
therapy--Some general considerations in view of work in this
field.
Next to Darwin, though by a wide interval, August Weismann (d. 1914,
_a.e._ 80) has most influenced general biological thought. His
failing eyesight at middle age caused him to abandon the microscope
for biological thinking, a field where there was a great need of
synthesis and expert theory and in which he developed great power and
influence. His hierarchy of metamicroscopic vital units, his dogma
of the non-inheritance of acquired qualities in confutation of the
prevailing Lamarckianism, and his demonstration of the continuity of
the germ plasm have been theses of great interest and centers of very
active discussion, even outside the special field of zoölogy, although
in the latter doctrine, which chiefly concerns this discussion, he
was in a sense anticipated by Owen, Jäger, Nussbaum, and especially
by Sir Francis Galton, as he later found.[164] He first set forth the
now generally accepted view that most of the primitive unicellular
organisms do not die and also sought to explain how death first entered
the world.[165] He says:
We cannot 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 the other, and neither of them
is older nor 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.
Each of these one-celled individuals thus lives on and grows, till
its surface, through which all nutritive substance is absorbed and
which increases at a less rapid rate than its cubic content, becomes
relatively too small, so that the creature can no longer be nourished
through it and the mature cell faces the alternative either to die
or divide into two halves; and, accepting the latter, becomes, by
division, two smaller daughter cells that, as the food-absorbing
surface becomes now relatively greater, are rejuvenated, although
their combined substance is exactly the same as that of the mother
cell of which they are simply bifurcations. As, thus, the substance
of the parent cells all goes over into the offspring resulting from
the fission, nothing is lost in the process, not even an envelope or
membrane, as Götte, Weismann’s chief earlier critic, thought was the
case in encystment. Thus there is no vestige or rudiment of a corpse.
Nothing is sloughed off. It is in this sense that such creatures are
immortal. They have gone on growing and dividing thus ever since
life began and will continue to do so until it ceases. Thus there is
a direct continuity from first to last that is unbroken by anything
that can be called death. If once and so long as these single-celled
creatures were the only or highest forms of life, death or anything
like it was unknown. In all this process, of course, nothing like
conjugation, mating, or fertilization occurs.
That this is not mere theory the experiments and observations of many
subsequent investigators, especially Woodruff and his pupils, have
shown. In thirteen and a half years he found paramecia had divided some
8,500 times, and the process is still going on as actively as at first.
Of these results Raymond Pearl[166] says, “If in 8,500 generations--a
duration of healthy reproductive existence which, if the generations
were of the same length as in man, would represent roughly a quarter of
a million years in absolute time--natural death has not occurred, we
may, with reasonable assurance, conclude that the animal is immortal.”
Thus it is that larger, older cells are constantly being regenerated
by spontaneous division and natural death does not occur among most
protozoa.
They simply grow and divide in an ever alternating rhythm and this was
the fundamental cadence in the song of life. If the large or mature
stage is, in any sense, a prelude of old age, division in the same way
represents rejuvenation. The latter is thus almost, although perhaps
not quite, as primordial as the phase of growth itself, and among the
most ancient and persistent of all the heritages that higher forms of
life received from the lower is this power to grow young. Thus the
systole and diastole of the heart of the _Zoölogos_ began. The monad
becomes a duad; the individual, a dividual, almost as inevitably as
the former grows; and the processional through this tiny life cycle
contains in it the promise and potency of countless other processes
that developed from it later. Thus even a colony of the far more
complex coral polyps may develop perhaps for thousands of years from a
single individual.
Now, while protozoa may occasionally conjugate and thus prelude a
higher form of reproduction and while the simpler metazoa may propagate
by fission or budding, reminiscent of the older way, the general mode
of propagation among many-celled organisms follows what seems at first
a very different law. In these forms a sperm cell or spermatozoön must
penetrate a germ cell or an ovum and then the zygote, or fertilized
egg, immediately begins to reorganize itself from within and to divide
into two, four, eight cells, etc.; and these divisions produce cells
not all exactly like the mother cell but differentiation begins.
In some species, as early as the first few divisions certain cells
are set apart as germ cells, devoted exclusively to the purpose of
reproduction. From these ova and spermatozoa arise. While others, far
more in number and aggregate bulk and increasingly so as we ascend the
scale of life, become more and more specialized for the production of
different organs, structures, and tissues. These gradually lose the
power to produce entire individuals. It is these that produce, and
their descendants that constitute, all the rest of the body, or soma,
and so are called the somatic cells. It is these and their progeny only
that die while the germ cells, a very minute portion of the entire
body in the higher forms of life, still continue, like the protozoa,
to divide and grow _in sæcula sæculorum_, and it is they that, in a
mundane sense, are immortal. Of course very few of the _circa_ four
hundred ova produced during the sex life of an average human female and
vastly less of the three hundred and forty billions of spermatozoa,
according to Lote’s estimate, produced by the average male[167] become
mature individuals. Most of them perish by the way and all those in the
body at its death perish, of course, with it. But sex cells, or rather
the germ plasm, even in the highest animals, including man, which
attain their goal and produce mature individuals of a new generation,
continuing to follow the old formula of eternal growth and division
though vastly slower, remain still deathless.
Thus life is a really unbroken continuum from its beginning to its end
and we are all connected, as it were, by direct physical participation
with the life of our progenitors. Each individual produces a few germ
cells that reach the goal of maturity and many somatic cells doomed
to death; and in the next generation each repeats the same process.
Some flagellate spores, for example, when they divide, lose only the
flagellum, which each new individual has to reproduce for itself and
this is the rudiment of the corpse that in the higher forms of life
becomes indefinitely more bulky and complex; while underneath all this
increasing punctuation by death, as it developed, the old plasmal
immortality still persists. On the other hand, all forms of fission and
agamic budding, so common a method of reproduction in plants and often
found in simpler forms of multicellular animal life, such as sponges
and coelenterates, are reminiscent of the protozoan fashion.
Thus we see that death came into the world not by reason of sin,
as theology teaches, but because of differentiation. As cells
acquired the power to produce more and more specialized organs and
functions they lost the power to reproduce the entire body and they
lost it progressively--almost in exact proportion as their power
of multiplication became specific. Thus, as we should expect, we
find in the early stages of this differentiation cells that can be
influenced toward the old general or the new and more specific powers
of reproduction. Yet back of all the fact remains that life itself is
essentially perdurable and that we can explain death better than we can
explain life. Death is thus not necessary or universal but is derived
and is, in a sense, a product of slow development; and we can conceive
a stage of evolution in which natural death did not occur at all but
was always due to external accidents. Indeed, Weismann goes so far as
to say that the difference between the germ and the soma is so great
that the latter, with all its fortunes, has little or no influence upon
the former; and by his doctrine that acquired traits and qualities
are not inheritable he seems to draw a hard and fast line separating
the mortal from the immortal parts or organisms. He also devoted the
greatest ingenuity in evolving an intricate scheme of biophores,
ids, idants, determinants, etc., inherent in germ cells, in order to
explain the phenomena of heredity. His studies have had great influence
in directing the attention of investigators to the most elementary
structures and functions of germ plasm and the remarkable changes
within cells that occur in the very earliest stages of embryonic
development; while, as we shall see, many of the most recent researches
have been directed, since his work was done, to the conditions under
which somatic cells in different tissues of the animal body can be made
to proliferate and grow, under carefully controlled conditions, more
than it was possible for them to do under conditions afforded them
while they remained parts of the body in which they were developed.
Here I deem it in point to observe that the adoption in its extreme
form of the theory of preformation versus epigenesis, or the
assumption that no qualities due to the experiences of the soma can
have any influence upon germ plasm or affect heredity, would be to
revert to views very like those of the old creationists. From Weismann
we may well lay to heart that this influence is very slow and slight in
any one or even a large number of generations, suggesting a very long
prehistory for the germ plasm of higher organisms. But to hold that
nothing in the recent past or the near future of the environment within
or without the individual can ever in the least affect innate qualities
is to throw ourselves into the arms of a fatalism that more or less
blights all the motives of reform and amelioration of conditions or of
educational influences in their widest scope. On the contrary, we hold
that the ultimate goal of all the improvements of life or mores is to
better heredity, that most precious and ancient of all the many forms
of values and worths, and that the degree in which they do this is the
final criterion of all really worthy endeavor in the world. If the good
life of a long series of generations of our ancestors does not in the
least tend to make their offspring a little better born and give them
some slightly better chance for a worthy, long, and happy life, quite
apart from all postnatal, parental, and other influences, the taproot
of all motivations for reforming human conditions is cut, and all
efforts in this direction become a little falsetto and every generation
must start again at the beginning.
Just now we are told that the whole domain of consciousness since
civilization began has had little influence upon the deeper and
older unconscious elements of human nature but no one among these
psychoanalysts has for a moment insisted that it had none. The moral in
both cases is simply that we must now make far larger drafts upon the
inexhaustible bank of Time and realize that in the one case, body, and
in the other, mind, is immeasurably older than we had deemed them to
be, that is, that both germ plasm and the unconscious have been very
long in the making and come to us charged with potencies innate in the
individual but very slowly acquired--in the one case by the ascending
orders of animal life from the first and, in the other, by man and
his ancestors. We certainly have not yet heard the last word from
zoölogy which, while stressing the hereditary factors, for example, and
individual longevity, must admit that old age in general is a more or
less acquired character. Before we do so, an important correlation, to
which I shall advert later, between these investigations and those in
the new field of the endocrine glands and the hormones that have such
new and marvelous power of speedy and profound influences upon so many
parts of and processes that go on in the body, must be made.[168]
One of the chief traits of old age is the loss of germ plasm with
its power of perennially regenerating life and this loss leaves the
soma to slow degeneration. As germ substance decreases individuality
generally increases, sometimes in the form of gross selfishness. As the
body becomes cadaverous or corpse-like and the springs of love begin
to dry up at their source, secondary sex qualities fade and the sexes
again become more alike, as in childhood, and the extremely senile
are but the husk or shadow of their former selves. Tenaciously as
life is clung to, it is at the same time felt to be less worth saving
either here or hereafter, for whoever heard of senile decrepitude
wanting to be continued beyond the grave. All ideals of a future
life assume a restoration of maturity if not of youth. Doddering,
desiccating senility has always been abhorrent to gods and men and
I know of no either imaginative or scientific writer who has even
attempted to describe the senium as it would be if prolonged to its
extremest conceivable term, when each organ and function slowly
ceased “altogether and nothing first”--ever shorter in stature, more
shriveled and emaciated in form, hairless, the voice shrunk to a
whisper, tottering, tremors, and then inability to work, move, or even
eat; abatement of all natural functions, the senses slowly becoming
extinct, teeth and the power of mastication gone, everything in a
stage of progressive involution, increasing paralysis of all receptive
or effector processes, offensive perhaps to the very senses of those
about, seemingly forgotten for the time by death itself, which the
poor victim perhaps longs for but is unable to command the means of
attaining, feeling himself useless and a grievous burden, a just living
mummy, torpid, neither really sleeping nor waking; and in the end with
every natural function sinking synchronously but so gradually that
observers could not be sure whether each slow breath or heart beat was
really the last or just when the Great Divide had really been crossed
where Sleep embraces its brother, Death. Something like this would be
the fate of the soma, after it had been abandoned by the germ plasm,
if a really natural death occurred, that is, if, by some of the many
disharmonies that pervade the body, some organ or part did not break
down before the others were worn out and drag them to its own doom,
which is what always really occurs in fact.
If we look at the matter from the more psychological and Lamarckian
viewpoint, suggested, for example, by the thesis of Hering, that memory
is the most fundamental trait of organized matter, a view elaborated by
Simon’s theory of mnemes and engrams, all experience is more or less
permanently registered on the most vital of living substances, which is
“wax to receive and granite to retain,” nerve and brain being the next
best organs of registration only acting more specifically; while the
most generic resultants of experience attain their ultimate goal of
being recorded in the structure or functions of the germ plasm and thus
becoming permanent acquisitions of the species or race. On this view
the apex of life is reached at that stage of it when the influence of
the soma upon the germ plasm is greatest. This, of course, ceases when
the latter takes its departure with loss of the power to propagate.
Thus of all the stages of life, old age and its fortunes alone can
never affect heredity. Individuals who live on do so only by the
momentum given by germinal energies transmitted from their parents, and
only the old are completely isolated from the main currents of the life
of the race. They have already died racially or to the phylum and only
await a second or individual death. Thus if any large number of such
individuals lived on for many decades, they would be an encumbrance;
and so Nature, always intent on the interests of the species and so
indifferent to the individual, has to leave them to their fate. They
may still alleviate individual conditions but can contribute nothing to
racial memories in the above sense. The species has “forgotten them and
they are of it forgot.”
* * * * *
Elie Metchnikoff (d. 1916, _a.e._ 71), a bacteriologist and the
successor of Pasteur, who approached the problem of old age from a very
different angle and collected many interesting data, was led by his
experiments and observations to a unique theory.[169] He first sets
forth the disharmonies in the life of animals and especially of man
in a way that seems pessimistic; but both his volumes are subtitled
“optimistic studies” because he finds hope at the bottom of the Pandora
casket.
Old age, he thinks, is not due to loss of the power of somatic cells
to divide or reproduce themselves but is “an infectious chronic
disease, whether manifested by degeneration or an enfeebling of the
nobler elements and by the excessive activity of macrophags,” the
latter being large wandering cells represented by the white blood
corpuscles and which he holds to be true phagocytes or scavengers,
which, instead of protecting as they were meant to do, are very liable
to turn on and destroy the higher elements of the body. They are thus
like an army raised and sent out to destroy menacing savages that
may turn and attack its own city. Old age and death, then, according
to Metchnikoff, are not due, as Blütschli thought, to the exhaustion
of some kind of vital ferment that protozoa and germ plasm have
pre-eminent power to make; nor to the mere accumulation of waste, which
the more always tend to dump upon the less vital elements of the body;
nor, as Delboeuf conjectured, to the precipitation of the substance of
organs, which always tend to revert to their inorganic bases; nor to
Roux’s hypothesis that organs are always competing with each other for
the available nutritive material, and that as and when there is not
enough to satisfy all, those that have to starve drag down the rest;
nor to the failure of the initial momentum given at impregnation; nor
to the fact that at the senium the body has passed beyond the reach of
the influences of sex and its products; but it is due to a very rank
and variegated flora or fauna of noxious microbes, and especially to
the toxic products they make, which tend to accumulate in the large
intestine, making it thus a very cesspool or latrine of the most
manifold infections.
Darwinists have stressed the advantages of the large intestine for
convenience and the avoidance of the necessity of leaving frequent
spoors by which animals might be tracked by their enemies. But many
species are without it or have it only in rudimentary form and in man
its removal by surgery results in no very serious impairment. We may
add, too, that more recently psychoanalysts have described the anus and
rectum and their functions as centers of various erotic activities,
especially but by no means exclusively in children. Here the waste
products of the digestive processes are dumped, awaiting removal, and
it has long been known that their undue accumulation caused not only
local troubles but general malaise, anxieties, and nervous and mental
tensions. Metchnikoff and his pupils showed that very soon after birth
noxious bacteria find their way to the large intestine and flourish
thereafter in great profusion, especially in constipation, and that no
cathartics can be relied on for permanent relief, salutary as medicine
has always and everywhere found them for mitigation of many diverse
ailments. It is the microbes that find their chief nidus here that
are the principal cause of old age and if an antidote to their lethal
action could be found Metchnikoff believes life could be very greatly
prolonged. He attempts to show that among not only mammals but also
birds, the species that have developed the large intestine are less
long-lived than those in which it is rudimentary, so that in animals
generally its relative size and individual longevity are inversely
as each other. Most of the digestive processes are completed before
food reaches this terminal part of the long alimentary canal and very
little save water can be absorbed through its walls, so that rectal
feeding contributes very little, indeed, to the total nutritive needs
of the body. But it is here that death finds its chief armamentaria
and establishes a receptacle, factory, or laboratory of poisons. Not
only are there many microbes that here feed on food residues and
occasionally pierce the intestinal walls themselves, but they produce
putrefactive products that are still more lethal. The chief of these
are phenol and indol, both very complex and due to the breaking down of
albuminoids, the chief element in meat, peas, eggs, etc. Young people
may for a long time show no trace of the deleterious effects due to the
absorption of these toxins, but the slight wear and tear of the tissues
they cause is cumulative. They produce in animals old-age effects in
kidneys, arteries, liver, lungs, muscles, testes, ovaries, and even
in the brain, for senility is due to the action of these bacterial
invaders and not to time or to wearing out.
So vital and rapidly growing are these bacteria that they would soon,
under favorable conditions, outbulk the entire body. But while their
numbers are kept down by lack of nutriment and other conditions,
nature provides no adequate antidote to their activity. This was found
by Woolman and was called glycobacterium, or the sugar-maker. It was
found first in the dog, and it can be cultivated in the laboratory
and introduced into the body. It transforms starch into sugar without
affecting the albuminoids and it is not, like sugar, absorbed before
it reaches the large intestine. Thus it is not sugar that is the
antidote but the lactic acid of its product and this is found in
nature in the bacillus of sour milk, a common article of diet among
Bulgarians, who seem to be the longest-lived people in Europe. The
results of experiments with this product, first upon rats and other
animals, Metchnikoff thought remarkably rejuvenating; and as all know,
many substances containing lactic acid were for a long time in great
favor, although expectations of its effectiveness have by no means
been fulfilled. The death of Metchnikoff himself, too, at the age of
seventy-one, who had long and diligently used his own panacea, did not
help the confidence of his disciples, for we can never forget the old
slogan, “Physician, heal thyself.”
In Sanger’s returns to his questionnaire,[170] as well as to my own,
one often finds people who use some form of this preparation and with
what they deem good results and Metchnikoff’s volumes show such a
unique combination of humanistic and scientific interests that they
have had wide popularity.
The problems, however, with which he deals are so extremely complicated
that his work may really be said to have propounded more problems than
he solved. He believed he had found and even named specific phagocytes
attacking most, but not all, of the main tissues and organs of the
body. Cohorts of them encamp about cells, very slowly absorbing their
substance and depleting their energies--some attacking muscles; others,
heart and arteries, etc.; others consuming the pigment cells of the
hair which, however, as Pohl showed, continues to grow as rapidly in
old age as in youth, as do the finger nails; others making the bones
porous and brittle by removing the lime from them and transferring some
of it to the walls of the arteries; some even specializing to attack
brain and nerve cells. We must fight fire with fire, and to do this we
must not only introduce the sugar-making bacteria but provide them with
food _in situ_ in order that they may do their great work of purifying
the cradle or breeding ground of noxious bacilli. Some of his disciples
are still enthusiastic enough to believe that just as we purified the
Panama Zone; as vaccination has almost annihilated smallpox, which
once caused about one-tenth of all deaths; as Behring’s antitoxin
has greatly abated the scourge of diphtheria; as Wright’s vaccine
has lessened death from typhoid; as Ehrlich’s salvarsan treatment
has done so much for syphilis, and as he and Wassermann hope may be
done for cancer--so we may yet find and learn how to use a specific
that, although it will not realize the dreams of those who once
sought an elixir of life, will nevertheless contribute to its perhaps
indefinitely great prolongation. This Metchnikoff does not hesitate
to call “the most important problem of humanity.” His ideal is what he
calls orthobiosis, which is “the development of human life so that it
passes through a long period of old age in active and vigorous health
leading to the final period in which there shall be present a sense of
satiety of life and a wish for death.” Mere prolongation of life in the
sense of Herbert Spencer is not in itself desirable. When the wish for
death comes, he thinks that under certain circumstances suicide would
be quite justifiable. Old age, he believes, will not only be greatly
prolonged but will become optimistic. Pessimism he finds commonest
among young men, while many avowed pessimists have become optimistic in
their old age. Young men will not so precipitately attempt to displace
the old, as he finds to be too much the case now, but the latter will
attain greater power and influence.
The constitution man has inherited from his anthropoid ancestors is far
from fitting his present environment. The greatest disharmony of all
is the morbid nature and brevity of the period of old age. Man does
not round out his prescribed cycle and develop in its final stage an
instinct for and love of death, as he should. He is expelled from the
school of life at all stages of its curriculum but always before the
final or senior year, until the fact that there was such a final grade
has been almost forgotten. It was because man felt himself prematurely
cut off that he developed all dreams of resurrection and of another
life. Had he completed his life here he would never have wanted or
dreamed of another. Had the involution that begins usually in the fifth
decade or earlier gone on normally, it would have made each stage of
the recessional no whit less delightful than those of the processional
of youth till, having withdrawn more and more from life and being in
the end quite satiated with it, the individual would have rejoiced
to see the limitations that separate him from ultimate reality fall
away until he merges, body and soul, into the cosmos from which he
came. Only the simplest organisms are immortal and as we ascend the
scale and develop a more complex soma, the more impossible does any
kind of immortality become. Metchnikoff seeks nothing of this sort but
would simply increase the number of years and enrich them in the last
phase of our existence so that, instead of being the pitiful remnant
it now is and instead of having to console itself so pathetically by
the puerile and unsubstantial figments that religions and philosophies
have given us, man would enter upon the full heritage that nature
intended for him. Thus the highest goal of all endeavor is to overcome
the present degeneration of senescence, to cultivate physiological old
age; and when this ideal is realized, more and more of the complex and
intricate affairs of social, industrial, political, and other forms of
life will be left to the old men, for these things require not only
technical training but, perhaps even more, the wide view, insight, and
common sense for which experience with life is the best school.
Metchnikoff was able to discover only two ideal cases of old people
in whom his “instinct for death” was well developed. But he believes
that as gerontology advances this instinct will not be the exception
but the rule and that the very nature of old age as we know it will be
radically transformed. At present we know little more of it than the
prepubescent child knows of sex or the embryo of its mother’s milk.
When the instinct for death is well developed, we shall long for it as
we do for sleep when we are fatigued, for old age is The Great Fatigue.
Many instincts of the young are reversed and pass over into their
ambivalent opposite at a later stage of life; and so the love of life
will, in the end, be transformed into the love of death. Both animal
and human parents devote their lives to the service of their offspring
during the period in which this is necessary; but when the latter are
mature, we often find a reversal of this instinct. Perhaps the intense
sensitiveness of ova and spermotozoa displayed in the phenomena of
chemotaxis and in the marvelous power of regeneration of lost parts
among many lower forms of metazoa, and the many phenomena that led
Haeckel to call the soul of cells immortal, are lost later as higher,
conscious psychic powers develop; and if so, this shows the marvelous
transformability of the primitive impulses that dominate simpler forms
of life.
Thus Metchnikoff is a humanist as well as a scientist. He sets down
faithfully what he saw through the microscope, but not content with
that ventures to indulge his speculative instincts and tell the world
what he thinks his discoveries mean for the practical conduct of life
and of mind--and that, too, in more or less untechnical terms that make
his ideas accessible to intelligent laymen. For him, as for Plato,
“philosophy is the art of preparing for death.” He even urged that
“the instinct for death seems to lie in some potential form deep in
the constitution of man,” and it was this he sought to develop. The
only basis for all modern forms of belief in immortality roots in a
platonic reminiscence of the processes of the deathless germ plasm,
and from this the old soma and the, no whit less, old psyche have
departed as far as possible. Psychic life, too, has its proximate
beginnings in the intense vitality of germ plasm and cells and from
these rudiments the adult human consciousness has so far developed
that our conscious psyche knows no more of it than it does of the
migrations or depredations of the phagocytes within the body. Man is
the most pathetic of beings because of the two tides whose ebb and flow
constitute his life--evolution and de- or in-volution, anabasis and
catabasis. He has failed, on account of the action of the intestinal
fauna within him, to achieve any adequate sense of appreciation, still
less enjoyment of the refluent currents. Man is thus deprived of the
nascent period in which this wooing of death is due to arise and does
not reach his true end or final goal. Dreamy illusions about it have
always haunted his soul as unsubstantial surrogates. When man now
in the making is finished, what we at present call old age will be
a sort of superhumanity, a new and higher story, and its completion
will spontaneously bring with it new and deeper insights; and he will
approach and finally enter Nirvana with the same zest and buoyancy with
which he now takes possession of life.
Crude and amateurish as often is Metchnikoff’s philosophy, his courage,
candor, and the strength of his convictions are commendable, and the
faith he adds to his knowledge is full of hope. From his ideal thinker,
Schopenhauer, he caught the flavor of the Vedanta and Upanishads but
he did not see how these very ideals also underlay the mystic hermetic
philosophy of the medieval alchemists and their royal art, as modern
symbolists like Hitchcock and Silberer interpret them; and to this I
shall revert later. If he overestimated the value of his panacea and
ventured into fields of other experts in which he was ignorant and
where he was often mistaken, he has at least made a very valuable
addition to the yet all too meager literature on senectitude, which all
thoughtful and intelligent aging people can read not only with profit
but with pleasure, if only they have escaped from the narrow limits
of orthodox Philistia. To have really edified this now ever growing
section of all civilized countries is a real culture service. His work
is uniquely inspired by a spirit psychologically very akin to that
which impelled Buddha when he set out on his mission of finding The
Way, stimulated to do so by the sight of an aging man and a putrefying
corpse.[171]
Charles Sedgwick Minot, an embryologist, (d. 1914, _a.e._ 62) devoted
most of his maturer years to a study of the phenomena of growth,
keeping and daily weighing many young animals, especially guinea pigs,
and he has left us a good compendium of his life work.[172] Stated in
the most general terms, he held that old age and death were progressive
phenomena that began in the individual with life itself, that the best
method of measuring vitality was the rate of growth, and that this
constantly diminishes and finally ceases. As soon as, for example,
guinea pigs recover from the disturbances caused by their birth, which
are great and last two or three days because they are born at a very
advanced stage of development, they add from 5 per cent to 6 per cent
to their weight during a single day. But this percentage diminishes, so
that by the end of the first month they add only 2 per cent; at ninety
days, only 1 per cent; and the diminution continues, rapidly at first
and then more slowly. Calculating the time to make successive additions
of 10 per cent, there are twenty-five of these additions; and not
until we reach the seventeenth addition do we find nine days or more
necessary. The twenty-second addition takes four days, the later ones
being somewhat irregular. The first ten per cent increment often comes
in two days.
Chicks, too, are born highly developed, and so lose during the first
day. Then the daily percentage of increase is greater than in the
guinea pig. From the sixth to the tenth day inclusive the average is
nearly but not quite 9 per cent; at the end of the third month, only
2 per cent. Rabbits are born very immature and, being less developed,
grow more rapidly. The average for males of the first five days of
growth is over 17 per cent. The rabbit thirty days old has about the
same daily percentage of increase as the new-born guinea pig. The human
child takes 180 days to double its weight; a horse, 60; a cow, 47;
goat, 19; pig, 18; sheep, 10; cat, 9½; dog, 8; rabbit, 6–7, these rates
depending, in part, on the quality of the mother’s milk.
In embryos the rate of growth is still more rapid. The increase in the
guinea pig in the first five days is 3,520 per cent, or an average
of 704 per cent daily. From the fifteenth to the twentieth day it is
1,058 per cent, or an average of 212 per cent per day. Thus the rate
of growth during the foetal period is far more rapid and it is more so
in the earlier than in the later stages of embryonic development. The
farther back we go, the more rapid is this rate. Thus his curves show a
very steep decline in the rate of growth, even in its earlier stages,
and this decline continues, although at an ever decreasing rate, to the
end. Thus from this point of view the younger creatures are, the more
rapidly they are dying. The weight of a fertilized germ he estimates at
0.6 milligram (and he tells us that 50,000 of these could go by mail
for a two-cent stamp). Thus the human embryo at birth has increased
5,000,000 per cent of its initial weight. Old age is merely the later
result of changes that have gone on at a diminishing rate ever since
the ovum from which we originated was fertilized.
Life is growth; the retardation of growth is old age; and its cessation
is death. “Senescence is at its maximum in the very young stages, and
the rate of senescence diminishes with age” (p. 250). The embryo in
its earliest stages rushes toward old age at an almost inconceivable
velocity, the new-born infant runs, the child walks rapidly, youth
saunters, the adult mopes, and old age only crawls on toward death. In
other words, the momentum of life given by impregnation at the age of
zero is retarded--most at first and with a diminishing rate at every
stage.
Something like this same paradoxical law holds, Minot believed, for
the human brain and mind. In one of his Harvey lectures he tells us
that the brain of a child at birth is but little differentiated. During
the first year it learns all the great adaptations in the physical and
human world: time, space, ego, etc. “It learns more during the first
year than in all the subsequent years of life” and from birth on the
power of learning is rapidly diminished. It declines very fast during
infancy, more slowly in childhood, etc.
Accepting Metchnikoff’s dictum that senility is atrophy and that
toxins of intestinal origin poison and debilitate tissues so that they
succumb to, if they do not actually attract, the predaceous phagocytes
(though not proposing his substitute of sour milk for religion and
philosophy), Minot points out that we are always throwing off dead
cells. Blood corpuscles collapse and are utilized by the liver; the
skin is incessantly shedding dead cells, as is the whole intestinal
tract and each organ; stature declines some 13 cm.; the brain loses
some 19 gms. in weight; the rate and depth of respiration sink; the
heart, although growing larger and from the age of prime to senility
beating some eight times per minute faster, is nevertheless obstructed
in its action by rigidifying arteries; the bones grow spongy and their
hard outer part becomes a thin shell; the muscle fibers decline both
in size and number, exercise being able to increase only the former
and not the latter; both structure and function go on to rigidity and
inflexibility after sufficient firmness and size have been attained,
till the part becomes too hard and inflexible to function and then is
shed as the ripened leaf falls in autumn. But none of these processes
are abnormal and hence death is in no sense a disease. Indeed, the
power of repair and even recuperation persists far more in the old than
has been generally recognized.
The more specific cause of what is generally called old age he
finds in the increase of the quantity and the hyperdifferentiation
of the structure of the protoplasmic envelope of the nucleus. This
protoplasm constitutes the body of the cell. In the earliest stages of
cytomorphosis, which follow impregnation, the total amount of nuclear
material increases fastest, while later and especially in the senescent
cells it is the protoplasm that does so. In the early stages of their
embryonic development, too, the cells differ relatively little; but
those that constitute the adult body differ so greatly that any skilled
observer can tell from which organ they came, whether from the brain,
muscle, skin, stomach, liver, etc.; that is, they differentiate more
and more as these organs mature. This differentiation is, however,
all on the way to death and is never reversible; that is, old body
cells never grow young. Nuclei change but it is the protoplasm that
changes the most and acquires a new structure, while the composition
of the nucleus not only changes less but always retains certain
fundamental traits. “The increase of the protoplasm, together with
its differentiation, is to be regarded as the explanation (or should
we say cause?) of senescence” (p. 134). This is necrobiosis. All old
cells, from whatever organ, are thus as recognizable as old faces.
“Growth and differentiation of protoplasm are the cause of the loss of
the power of growth” (p. 161). He even holds that the first stages of
the segmentation of the ovum must be called rejuvenation. On page 167
he says:
The life of the cell has two phases--an early brief one
during which the young material is produced and the later
and prolonged one in which the process of differentiation
goes on; and that which was young, through a prolonged
senescence becomes old. I believe these are the alternating
phases of life, and that as we define senescence as an
increase and differentiation of the protoplasm, so we must
define rejuvenation as an increase of the nuclear material.
The alternation of phases is due to the alternation in the
proportions of nucleus and protoplasm.
In adults, and even in the old, there are always young cells in
reserve, often grouped in certain foci, for example, the marrow of the
bones, which can in emergencies come forward, take up the function
of growth, regenerate lost tissues or, in lower animals, even lost
organs. At and even after the death of the aged there are always cells
and even parts that are relatively young and growing. There are also,
of course, the cells and their matrix, which are very early set apart
for the purpose of reproduction, and these, of course, are least of
all differentiated. Most cells of the body, however, follow the law of
genetic restriction. This means that as differentiation proceeds, the
possible directions in which cells can develop become more and more
limited till finally they cannot divide at all and lose even the power
of nourishing themselves, and so die. The cell and all of it represents
life, and Minot has no use for any of the smaller metamicroscopic vital
units, gemules, plastidules, plasomes, ideosomes, granules, etc., but
thinks that if we wish to accept any kind of ultimate elements of this
sort, Weismann’s scheme of them is perhaps, on the whole, the best.
As to the practical questions, how we can help rejuvenation and delay
senescence, he states that he has nothing to suggest, although he
believes it possible that some time in the future a means may be found
of increasing the activities and volume of the nucleus and restricting
the growth and differentiation of the protoplasm, which would mean a
prolongation of youth.
Minot concludes his volume with a glance at paidology in order to
stress the great relative importance for both the bodily and mental
development of the early stages of life. The baby develops faster than
the child; the child, than the youth, etc., and the rate of psychic
unfoldment declines very rapidly from the first, as does that of the
body. Week by week, from birth, there is a remarkable expansion of
life. Each one of the senses learns how to function effectively and
most of them learn to attract the attention, the power of correlating
movements and making voluntary ones, and the rudiments of memory
and association are laid down, as are the bases of disposition. The
infant from the earliest months of its life knows much of the persons
and objects in its environment and perhaps has even discovered its
own ego. It touches, handles, tastes everything; is an inveterate
investigator in an ever widening field of research; has at least a
sense of intercourse and companionship; is already at home with time,
space, cause, and relation; its feelings, will, and even intellect are
developed, and in this order; and the foundations for knowledge and
achievement are laid. Thus the child of school age is already senile
so far as its infancy is concerned and the boy’s psychic processes are
retarded, hard, and unspontaneous. Learning begins to be difficult.
Nature no longer shoots the mind up the phyletic ladder but it must
climb and grow henceforth by work as well as playwise. Thus man’s
mental powers show the same law of progressive retardation as does his
physical growth. Instead of drawing the dead line at forty, as Osler
did, Minot draws it at twenty-five. Had he been versed in paidology or
even known the Freudian conceptions of infancy, he might have greatly
amplified his treatment of this stage of the psychic life with which
his volume closes. But as it is, there are certain definite criticisms
of his conclusions concerning gerontology.
First, as I have said, he only attempts to show the cause and has
nothing to say as to the cure of senescence. But he was not in quest of
a panacea and was too true to the limitations of his science to pretend
to have found one. This will be a disappointment only to those laymen
who read him in furtherance of this pragmatic quest.
More serious is the objection that, according to his criterion and
curves of declining growth rate, we are really old when we stop
growing, for the mature young man and the very old one both are living
but a very little above the deadline. On this view, the extinct
saurians that grew all their lives were far more vital than creatures
that attain a relatively fixed and constant size early and then stop
growing. Growth is one measure of vitality, but surely function is
another. The dynamic curve of energy and the power of work rises
rapidly as that of growth declines and the curve of brain work reaches
its apex somewhat later. Determining the increment of pounds or even of
foot pounds of energy is not the sole measure of vitality.
Again, if all differentiation is progress toward death, evolution
itself, instead of being progressive, is really retrogressive and
the ascending orders of life are only a funeral march to the grave.
Minot admits this in principle but says that although the advance it
brings is bought at the price of death, it is worth all it costs.
So it is, but it will not be if the organization and its increase in
heterogeneity of structure are only morphological. It pays because
of the quest for the good, the beautiful, and the true; because of
science, law, love, the control of nature, the organization of society;
because of the supreme joy of just being alive and the exhilarating
sense of progress. The more evolved all creatures are, including man,
the more the pleasure field overlaps the field of pain.
As the hypercivilized mind often longs back, like Rousseau, to an
idyllic state of nature; or the world-weary pietist longs back to
God; and, we may now add, as the psychoanalyst finds what he deems
a psychodynamic equivalent for this trend, in a perhaps yet more
exaggerated form, in the flight from reality, seen in dementia præcox
and in longing for the mother’s lap and, as Ferenczi says, even for
her womb; so Minot’s view of life might almost justify a kind of
homesickness for the state of the ovum or the immortal germ plasm, for
in this state of incipiency a single-celled organism performs all the
functions of life, not only nutritive and reproductive but sensient
and motor. It is at this stage, when all cells do all things, that the
spirit of life celebrates its highest triumph. The sigh for lost youth
is here deepest. Life itself as we know it from this viewpoint seems a
little falsetto and pathetic, for it is throughout, in a sense, a fall.
The analyst is also tempted to venture a little farther and to raise
the question whether the life of the author of this view itself did
not subconsciously contribute a little to reinforce his theory. With
a none too rich and full childhood and youth, waiting for years for
adequate recognition, passionately if not precociously devoted to the
study of embryology, in which field he became one of the ablest and
most accomplished of all leaders,[173] it would not be surprising if
he found certain compensations in devoting his life to a study of that
stage in which its manifestations are most active, and ably developed
in this field apperception centers he somewhat overworked, while his
self-affirmation and the instinctive impulse we all have for due
recognition give a subtle self-satisfaction in reiterating the paradox
that death is most active near the beginning rather than the end of the
life cycle. Whether this suggestion has any validity or not, no one has
ever more challengingly presented the problem of why the rate of growth
declines from first to last, and whether it be due to an inevitable
loss of the initial momentum or biological _élan vital_ or to checks,
arrests, and inhibitions of it, some of which may be removed. The very
intensity of its early manifestations, if it gives us a haunting sense
of loss also reinforces the hope that the high potential with which
we all started somehow, sometime, may be better conserved, so that
perhaps here, again, as with Metchnikoff’s views, the morale of Minot’s
conclusions is, on the whole, optimistic.
* * * * *
Charles Manning Child, professor of biology in the University of
Chicago, has given the most comprehensive statement of his problem to
date from the standpoint of his science, although, as we shall see,
much has been done since.[174] His most interesting and important
contribution for our purpose is his refutation of the older view that
life is always a progressive process and that true rejuvenescence
does not occur. Of course, in higher animals the progressive features
are predominant and development ends in death. But the above
generalization does not take due account of what occurs in lower
organisms, while even in man and other mammals the different tissues
do not undergo senescence either alike or synchronously. Some, for
example, cells of the epidermis remain relatively young till and after
the death of the individual. In other tissues such replacement of old,
differentiated, or dead cells by younger ones occurs more or less
extensively and tissue regeneration following injury occurs more or
less in all tissues save only the nervous system. Such regeneration
retards the aging of the tissue or organ as a whole. Minot thought
that in such cases regeneration arises from cells or parts of cells
that have never undergone differentiation, so that even in such cases
development is progressive and not regressive. Even if he is right in
maintaining that fibrillar substance cannot regenerate, it must be
noted that new fibrillar substance does arise in continuity with the
old, while isolated cells apparently do not produce it. Child maintains
that there is differentiation in such cases and that these regenerating
cells have returned to a kind of activity characteristic of the early
stages of embryonic development; that is, that cells _can_ assume an
activity characteristic of an earlier stage. “Even in the outgrowth
of new nerve fibers from the central stump of a cut nerve there is
return to a process of growth and development which is normally
characteristic of an earlier stage of development.” Thus regression and
differentiation do occur in most tissues of man and higher animals,
although cells of one tissue can never produce those of another.
Again, after hibernation regeneration is often extensive. The large
proportion of young cells in the body in such cases renders the
animal as a whole appreciably younger than at the beginning of
hibernation, so that the periodic cycle of activity and hibernation
is much like an age cycle. This rejuvenescence may begin during the
hibernation, when the animal is living on its own substance. Again,
we see periodic changes that resemble the age cycle in glands. In
the pancreas cell, for example, the loading of the cell is both
morphologically and physiologically similar to senescence, and the
discharge, to rejuvenescence. In this case the change occurs in
individual cells without cell reproduction. Even the cells of the
nervous system throughout mature life possess no appreciable capacity
for differentiation and regeneration beyond the power to regenerate
fibers arising from them. Child believes that the effect of a change in
mental occupation or of a vacation may afford “some slight degree of
rejuvenescence of the nerve cells.” Verworn, he tells us, distinguishes
between fatigue due to accumulations that check metabolism and
exhaustion due to lack of oxygen, both of which may cause senility
in nerve cells. “Thus exhaustion resembles senility as death from
asphyxiation resembles death from old age.” Recovery from exhaustion
is not the same sort of change as rejuvenescence except as it involves
increase in the rate of oxidization. But fatigue and recovery
constitute a cycle resembling closely the age cycle.
Studies of starvation suggest the same thing. Various experiments have
shown that in the later but premortal stage of starvation there is
a certain activation of vital processes, including heat production,
and it is possible that this has some significance for regeneration.
Higher animals are apparently unable to use their own tissues as a
source of nutrition to any such extent as the lower forms can do, and
this is probably connected with a higher physiological stability of
the tissue components. The body weight often does, however, increase
and become greater after starvation than it was before, so that a
fasting period is followed by an increase in vigor and body weight and
hence the wide belief in its therapeutic value. On the other hand, the
injurious effects of over-nutrition in man are supposed to be due to
the accumulation of food or to intoxication, but it is possible that
overnutrition actually increases the rate of senescence by augmenting
in the cellular substratum not only the decomposition of food but other
substances that decrease the rate of metabolism. There are certainly
many instances of longevity in man on a low diet. Again, after certain
bacterial diseases, for example, typhoid, the body weight often becomes
greater and vigor increases. While low diet often does good, it may, on
the other hand, aggravate many diseases. Frogs and salamanders may live
a long time without food and undergo great reduction, and starvation
sometimes has a directly rejuvenating effect. The animals grow much
more rapidly afterward and use a larger percentage of nutrition in
growth and attain a larger size than those continuously fed.
Death of cells apparently from old age occurs at every stage of
development and many cells do not die when the individual does,
for he does so only because some tissue or organ that is essential
reaches the point of death. Some have thought glands are primarily
responsible for it; but others, whose view Child adopts, hold that it
is the nervous system, especially its cephalic part, that dies first
in man. In various insects and, for example, the salamander, death
occurs almost at once after the exclusion of the sexual products, but
this is exhaustion. In most, the length of life of the individual is
determined by that of the shortest-lived essential organ or of the
tissue that is least capable of regression and rejuvenation and the
development of which, therefore, remains most continuously progressive.
In cold-blooded animals where the rate of metabolism is dependent
on external temperature, senescence can be reduced by cold, and in
certain lower invertebrates by the simple method of underfeeding. When
cells lose the capacity to divide, they differentiate, grow old, and
sooner or later die, although death everywhere is the result of final
progressive development if this process goes far enough and is not
interrupted by regression caused by the need of repair, reproduction,
or lack of food. Death is due, thus, to increased physiological
stability of the substratum of the organism or to an increasing degree
of differentiation that this general stability makes possible. And as
individuation increases, death becomes more and more inevitable. Rubner
calculated the total energy requirements in calories for doubling the
body weight after birth and the requirements per kilogram in body
weight for the whole period of life, for a number of domestic animals.
His totals for all, except man, showed close agreement, and hence he
concludes that the amounts of energy required are the same in all
species except for man, who has a far greater amount of energy, that
is, a smaller percentage of the energy of food is consumed in growth
and maintenance of body weight and more in activity than in other
animals. Very likely domestic animals expend less energy than their
wild congeners but it is certainly difficult to correlate these results
with Minot’s criteria of age as measured by the decrease of growth.
Child concludes that senescence is more continuous in man than in the
lower forms. His long evolution has given a physiological stability to
the protoplasmic substratum and a high degree of individuation results
from this. But the central nervous system, being least capable of
progressive change, always dies first, so that the length of man’s life
is that of his nervous system and physiological death and senescence
inhere in its fortunes. In the lower forms the death point may never be
attained under normal conditions because of the low stability of the
substratum and the consequent decrease of individuation that permits
the frequent occurrence of a high degree of rejuvenation. But in the
higher forms of life the capacity for the latter is limited by greater
stability; and this, again, has been acquired through a process of
evolution lasting through so many millennia that we must certainly
“admit that this task [man’s rejuvenation] may prove to be one of
considerable difficulty.”
Thus, according to Child, whose views are the most philosophical
and insightful in the field of biology up to date for our purposes,
senescence and rejuvenescence are both going on all the time in
all cells and organs and are not special processes. In most cells
and in most lower organisms dedifferentiation and despecialization
of structure and function, which we may term in general regressive
tendencies, are always less pronounced than progressive impulsions,
while the latter predominate still more in the higher forms of life.
It is “quite impossible to account for the course of evolution and
particularly for many so-called adaptations in organisms without the
inheritance of such acquired characters, but since thousands or ten
thousands of generations may be necessary in many cases for inheritance
of this kind to become appreciable, it is not strange that experimental
evidence upon this point is still conflicting” (p. 463). Germ plasm is
not something apart from or uninfluenced by all that goes on in its
immediate environment within the body. Regression and dedifferentiation
involve reconstitution and always approximate reproduction. To state
the matter roughly, all processes involved both in growing old and
in growing young might conceivably be arranged on a kind of Porphery
ladder with agamic forms of indefinite reproduction, as illustrated in
unicellular organisms or in germ plasm at the lower or _summum gens_
end, and the most differentiated cells that have progressively lost the
power of reproducing the whole organism, regenerating lost parts, power
to grow, divide, and nourish themselves, at the top of the ladder,
representing the _infima_ species. On such a ladder, development,
differentiation, and individuation is progress up, and all rejuvenating
activities are descent toward the most generalized function of
perpetual self-reproduction. This conception is in very suggestive
harmony with the analogous psychoanalytic law of restitution to mental
health by reversion to a more primitive state of psychic development,
for all these methods might be called rejuvenation cures.
Physiological integration, with its increasing stability of the
structural substratum, makes senescence cumulative as we go up the
scale of evolution, so that it is ever less balanced or offset by
rejuvenation, reproduction, or other regressive changes, as is the
case with simple organisms whose life cycle consists merely of
brief alternating phases of progression and regression, for the
large protozoan cell about to divide is old compared with the two
smaller daughter cells formed from it. Senescence is retardation
and rejuvenescence is the acceleration that works by transforming,
readapting, and even sloughing off old and useless structures. It will
take long to modify the course of evolutionary processes that are the
result of millions of years of alternating progressive and regressive
changes, but not only the phenomena of rejuvenescence but “sports”
and saltatory mutation, to say nothing of the findings of recent
experiments showing how life and even activities of somatic cells
separated from the body and given a more favorable environment may be
indefinitely prolonged, point toward a vast reservoir of vitality. Thus
we come to a new appreciation of the incalculable energy behind all
the phenomena of animate existence and the hope is irrepressible that
somehow, although we have as yet no idea how or when, we may abate or
inhibit the forces that check or repress it and man may emerge into a
fuller and even a longer life.
* * * * *
Jacques Loeb, of the Rockefeller Institute, has devoted himself for
many years, with a rare combination of great learning and originality,
to problems directly or indirectly bearing upon old age and death.[175]
As his studies of tropism show, he is prone to mechanical and chemical
interpretations; and since science has more or less eliminated
smallpox, typhoid, yellow fever, malaria, rabies, diphtheria,
meningitis, etc., the citizens of scientific nations will sometime,
he thinks, be guaranteed a pretty fair probability of a much longer
duration of life than they now enjoy. If we define life as the sum of
all those forces that resist death, which means disintegration, the
latter is comparable to digestion, which transforms meat into soluble
products by two ferments, pepsin in the stomach and trypsin in the
intestine. These ferments break up the mass into molecules small enough
to be absorbed by the blood, and both of them exist not merely in
digestive organs but probably in all living cells. They do not destroy
our body, perhaps because the coöperation of both is required to do
so and this is possible only at a certain degree of acidity, which
cannot be reached in the living body because respiration is constantly
removing acid. Death thus really comes when respiration ceases.
Of course there is another cause of disintegration, namely,
microörganisms from the air and in the intestines. During life the
cells are protected by a normal membrane that is destroyed in death
and then the action of the microörganisms can superpose itself upon
that of digestion. Thus in man death is stopping the breath and this
may be done by poison, disease, etc. The problem is whether there is
any natural death, for if not we ought to be able to prolong life
indefinitely. But we cannot experiment on man because neither the
intestines nor respiratory tract can be kept free from microbes.
A Russian, Bogdanow, solved this problem for the fly, putting its
fresh eggs into bichlorid of mercury, which a few survived, with no
microörganisms on the outside. These eggs were then developed on
sterilized meat in sterile flasks and Guyemot raised 80 generations
of fruit flies thus. Loeb himself and Northrop raised 87 generations.
Their dead bodies were transferred to culture media such as are used
for the growth of bacteria and more were produced thus for years. Hence
fruit flies freed from infection and well fed would not entirely escape
death and probably higher organisms would thus die from internal causes
were external ones excluded. Eggs, for example, those of starfish,
ripen and disintegrate very rapidly if not fertilized by the process
of autolysis, which acts only after the egg is ripe. The fertilized
egg, however, does not degenerate in the presence of oxygen but dies
in its absence, so that we might say that the fertilized egg is a
strict aërobe and the unfertilized, an anaërobe. The entrance of the
spermatozoön saves the life of the egg.