MORE ABOUT SUSPENDED ANIMATION
I gave some account in the last chapter of the experiments made within
the last twenty years, which have shown that, in certain very simple
organisms and in seeds, all chemical change can be stopped by the
application to them of methods of freezing. The continuous changes
which go on in these living things under ordinary circumstances are
arrested by the solidification of what was more or less "moist"
material. Water in the liquid state, though it may be in extremely
minute quantity, is necessary for the chemical combinations and
decompositions which go on in living things. Hence not only the
solidification of all moisture, in or having access to the living
bodies experimented on, arrests those chemical combinations and
decompositions, but very thorough drying also has this result. Yet
either on thawing the frozen liquid or supplying moisture to the "dried
up" organism, the previously continuous chemical and physical changes
are resumed as though no arrest or suspension of them had occurred. No
limit is known to the length of time during which this arrest may be
continued, and yet a resumption of living changes occur when the cause
of arrest–namely, either solidification by cold or else dryness–is
removed. The apparatus–the exact structure and the exact chemical
materials–of the seeds or the bacteria remains uninjured and unchanged
by either freezing or drying carefully applied. It is, of course,
impossible to guarantee that no accident, no unforeseen change in the
surroundings, shall take place and destroy in one way or another the
experiment. But the arrest of all change, such as goes on in life, has
been, in many experiments, maintained under careful supervision and
protection for several months, and yet life has been resumed when the
cause arresting chemical change has been removed. The presumption,
then, is in favour of the possibility of the arrest being maintained
for an unlimited period, and yet at any time being resumed when the
arresting cause (cold or dryness) is removed.
Before what we may call "the suspensory action" of very low
temperatures had become generally known, the question occurred as to
whether seeds kept in a dry condition for several months, or even
years, and yet capable of germination when placed in moist earth,
are during their dry condition undergoing any chemical changes. The
matter presented itself in this way. The dry seeds can germinate when
sown, therefore they are not dead, but living. According to various
physiologists and philosophers (_e.g._, Herbert Spencer), life is
a continuous adjustment of internal to external relations. Burdon
Sanderson, the Oxford professor of Physiology, declared that "life is
a state of ceaseless change." If this is a correct conception, and if
by "living" we mean, as the great Oxford English Dictionary tells us,
"manifesting the property called life," then the seeds which, though
dry, are still "living" or "alive" or "endowed with life," should yield
some evidence of the "ceaseless change" (by which is meant chemical
change) of which, as things not dead but living, they are supposed
to be the seat. The late Dr. George Romanes published in 1893 some
experiments on this matter. We know that free oxygen is very generally
(though not universally) necessary for the continual chemical changes
which the minutest as well as the largest plants and animals carry on.
Romanes enclosed a quantity of dry seeds in glass tubes, from which he
pumped out all gas as completely as possible–that is to say, all except
one-millionth of the original volume. He also expelled all oxygen by
replacing it by other gases. As a result of this treatment, continued
for as much as fifteen months, he found that neither a high vacuum nor
subsequent exposure for twelve months in separate instances to oxygen
or to hydrogen, or nitrogen, or carbon monoxide, or carbon dioxide,
or hydrogen sulphide, or the vapour of ether or of chloroform, had
any effect on the subsequent germinative power of the seeds employed.
These experiments proved that anything like respiration by ordinary
gaseous exchange with the atmosphere was _not_ going on in the seeds,
and that if they are the seat of "ceaseless change" because not dead,
the changes must be chemical interactions of some kind or other within
their protoplasm.
The keeping of seeds and also of bacteria for days and even months–at
temperatures as low as 100 degrees below zero centigrade–and their
subsequent resumption of life, has removed the possibility (not
excluded by Romanes) of the occurrence of chemical interactions within
the substance of these organisms preserved during long periods of
time, and yet not ceasing to be what is ordinarily called "alive,"
or endowed with "life." It is time that we should definitely abandon
Herbert Spencer's and Burdon Sanderson's definitions or verbal
characterizations of "life." The word "life" is commonly and properly
used to designate the condition of a "living thing" or a thing which
is "alive." A thing which has lost life–that is, which was living, but
is so no more, and cannot be "restored to life" or resuscitated–is, in
correct English, said to have "died," or to be "dead." The motionless,
unchanging frozen seed or bacterium, which resumes its living
activities when carefully thawed, has _not_ "died." The mere fact that
it can be resuscitated justifies the application to it, according to
correct English usage, of the word "alive"–it is still "alive." It is
not possible to alter the significance of the words "life," "living"
and "alive," so as to retain the definitions of Herbert Spencer and
Burdon Sanderson as correct. They are incorrect. Life is not continuous
or ceaseless change. It is a property of the more active substance of
plants and animals which has special structure and definite chemical
constituents. The property is, no doubt, usually manifested under
normal conditions of temperature, light, moisture, pressure, chemical
and electrical surroundings in a continuous series of changes, both
chemical and physical. But at exceptionally low temperature, and in
other arresting circumstances these changes can, in a few exceptional
organisms, be absolutely stopped, though the organism in which the
changes cease is uninjured as a mechanism. It still possesses "the
property of life"–is still "alive" although motionless and unchanging.
Its life is in suspense, as is that of a clock with arrested pendulum.
The unjustified conception of "life," or "living," or being "alive,"
and not dead, as necessarily a state of incessant chemical and
other change, is bound up with the old fancy that life is not to be
considered as a state or motion of a special and complex structure
called protoplasm, but is a thing, a spirit or an essence, which takes
possession of organic bodies and makes them "live." According to Sir
Oliver Lodge, if chemists could build up the chemical materials which
constitute protoplasm, the protoplasm so made by them would not live.
It would (he stated at the meeting of the British Association in
Birmingham in 1912) have to receive a charge or infusion, as it were,
of this thing suggested by the word "life." It cannot live itself
(according to the suppositions of Sir Oliver), but serves as the
vehicle, the receptacle, for this supposed intangible entity "life." In
the same imaginative vein, our grandfathers used to say that heat was
due to the entity or "fairy" "caloric" which could be enticed into or
driven from material bodies, making them "hot" by its presence and cold
by its greater or less exclusion. The suspended animation of frozen
germs and their return to life when warmed could thus be represented
as an affection or affinity between the fairy "Vitalis" and the fairy
"Caloric," the former fleeing from the body and waiting near when the
latter deserts his place, but returning to happy union with "Caloric"
when he again, however feebly, pervades once more the vehicle provided
for "Vitalis." Such imaginary essences are not of any assistance to
us in arriving at a knowledge of the facts, and so far from helping
us to a comprehension of the ultimate nature of things (which we
have no reason to suppose that it is possible for us to attain)
their introduction tends to the substitution of imaginary causes and
unverified assumptions for the carefully-tested and demonstrated
conclusions of science.
In 1871 Lord Kelvin, when president of the British Association,
suggested that the origin of life as we know it may have been
extra-terrestrial, and due to the "moss-grown fragments from the
ruins of another world," which reached the earth as meteorites. It
was objected to this that the extreme cold–very near to the absolute
zero–which prevails in interstellar space would be fatal to all germs
of life carried by such meteoric stones. But twenty years later Sir
James Dewar showed that this objection did not hold, since at any
rate some forms of life–certain bacteria–could survive an exposure of
several days to a temperature approaching the absolute zero. Later Sir
James made some very striking experiments by exposing cultivations of
phosphorescent bacteria to the temperature of liquid hydrogen (252
degrees below zero centigrade). These bacteria may be obtained by
selective cultivation from sea-water taken on the coast, in which a few
are always scattered. A rich growth of these bacteria in gelatine broth
gives off a brilliant greenish light when shaken with atmospheric air
or otherwise exposed to oxygen. The light is so intense that a glass
flask holding a pint of the cultivation gives off sufficient light to
enable one to read in an otherwise dark room. The emission of light
is dependent on the chemical activity of the living bacteria in the
presence of oxygen. In the absence of free oxygen they cease to be
luminous. As soon as they are killed the light ceases. When they are
frozen solid the light ceases, even in the presence of free oxygen
gas. When a film consisting of such a culture is frozen solid it will
remain inactive if the low temperature be maintained for months, though
exposed to free oxygen gas, and then, as soon as it is liquefied by
a gentle rise in temperature, the active changes recommence, and the
phosphorescent light beams forth. Sir James Dewar exposed such films
to the low temperature of liquid hydrogen for (so far as I remember)
six months, and obtained from them at once the evidence of their living
chemical activity, namely, their "phosphorescence," as soon as they
were thawed. In the frozen state, at a temperature of minus 250 degrees
centigrade, nothing, it appeared, could injure these phosphorescent
bacteria. No chemical can "get at them" at that temperature, the most
biting acid, the most caustic alkali cannot touch them when, like them,
it is in a hard, solid condition. Powdering the film by mechanical
pressure has no effect on the bacteria. They are too small to be
crushed by any mill. Such germs would, it seemed, surely be able to
travel through interstellar space, as suggested by Kelvin.
Then it occurred to Sir James that light–the strangely active
ultra-violet rays of light–might be able to disintegrate and destroy
the bacteria, even when frozen solid at the lowest temperature. He
exposed his frozen cultures to strong light, excluding any heat-giving
rays, and found that the bacteria no longer recovered when subsequently
the culture was thawed. Light, certain rays of light, can, it thus
appears, penetrate and cause destructive vibrations in chemical bodies
protected from all other disintegrating agencies by the solidity
conferred by extreme cold. I am not able to say, at the moment, how
far this important matter has been pursued by further experiment, nor
whether what are called the "chemically active" rays of light and
other rays such as the Röntgen rays can effect chemical change in
other bodies (besides living germs), upon which they act at normal
temperatures, but in regard to which they might be expected to be
inoperative when the bodies in question are brought into the peculiar
state of inactivity produced by extreme cold. Since light is far more
intense outside our atmosphere than within it, it seemed, at first,
that the demonstration of its destructive action on frozen germs puts
an end to Kelvin's theory of a meteoric origin of life. It must,
however, be remembered that minute living germs could conceivably be
protected from the access of light by being embedded in even very
small opaque particles of meteoric clay. So Lord Kelvin's suggestion
as to the travelling of life on meteoric dust cannot be set aside as
involving the supposition of the persistence of life in conditions
known to be destructive of it.
The great interest in former times in relation to "suspended
animation" has naturally been in relation to the occurrence of this
condition in man and the possibility of producing it in man by this
or that treatment. There is no doubt whatever, at the present day,
that "death-like" trances, whether occurring naturally or after the
administration of drugs, in the case of man and of higher animals,
are not due to that complete suspension of living changes which we can
produce, as I have here related, in certain lower forms of life. These
death-like trances are merely cases of reduction of the living changes
to a very low degree.[6]
The bodies of all but the simplest animals and plants are too large and
too complex to survive the bursting and disruptive action of extreme
cold, due to the unequal distribution of water within them and its
irresistible expansion when frozen. Their living mechanism is broken,
mechanically destroyed by this expansion. We cannot hope to apply
cold to man so as to produce "suspended animation." It is true that
experiments are on record in which fish and even frogs have survived
enclosure within a solid mass of ice by the freezing of the water in
which they were living. But careful experiments are wanting which
would demonstrate that these animals were actually frozen through and
through, and that either fish or other cold-blooded animals can survive
a thorough solidification by freezing of their entire substance. Such
survival cannot be pronounced to be impossible, but it has not been
demonstrated in any cold-blooded animal–even shell-fish or worm or
polyp–let alone a warm-blooded mammal. It appears that, apart from
disruptive effects, the protoplasm of even very minute and simple
organisms, such as the Protozoa, does not in all kinds, even if in any,
survive exposure to great cold. The toleration of great cold and return
to living activity after thorough freezing is, it appears, a special
quality attained by the living material of vegetable seeds and by many
kinds of bacteria. A similar special toleration of high temperatures,
a good deal short of the boiling point, but high enough to kill most
plants and animals, is known to characterize certain bacteria and
allied Schizophyta found in hot springs. It is a matter of common
knowledge that many animals and plants are killed by a temperature
(whether too high or too low for them) which allows others to flourish
and may be necessary for their life. Minute organisms (flagellate
monads) have been cultivated experimentally in a nourishing liquid, the
temperature of which was raised daily by one or two degrees until the
liquid was so hot that the same species of organism was at once killed
by it when abruptly transferred to it from liquid at ordinary summer
temperature.
The true "suspended animation" of many vegetable seeds and of many
kinds of bacteria under the influence of cold is not an exhibition of
a general property of living things, but is due to a special quality
of resistance gradually attained by natural selection of variations a
little more tolerant of cold or of drought than are the majority. It is
of life-saving value and a cause of survival to the species of plants
and bacteria concerned. No doubt there is need of further experiment on
the subject of the "killing" or destructive effect exerted by different
degrees of diminution of temperature upon the protoplasm of all kinds
of organisms, and with the knowledge so obtained we shall be able to
frame a conception of the actual mechanical and chemical peculiarities
of the protoplasm of those bacteria and of those vegetable seeds
which can be exposed to the extreme of cold for many months or for an
indefinite period and yet subsequently recover or live again. Probably
in order to survive freezing, protoplasm must be, not absolutely dry,
but free from all but a minimum of moisture.
FOOTNOTE:
[6] See the chapter on "Sleep," in my "Science from an Easy Chair,"
Methuen, 1909.