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.