FOOTNOTE:
[5] For some account of "cilia," see "Science from an Easy Chair," Figs. 29, 33, 40 and the accompanying text.
CHAPTER XIV
MORE ABOUT WHEEL ANIMALCULES
MICROSCOPIC as the wheel animalcules are they yet have been watched and examined by their admirers to as great a point of intimacy as that reached by the devotees of insects or of birds. A remarkable fact about them is that in about 130 different species (out of the 500 known) it has been found that the males are diminutive creatures, about one-tenth the size of the females, and devoid of digestive canal; in fact, little more than minute swimming sacs full of spermatozoa. In one group, that of the crawling Rotifers, to which the common wheel animalcule, figured in the last chapter, belongs, no male at all has ever been discovered. They are all females. They are precisely those wheel animalcules which are known to microscopists for their power of surviving (like the little water-bears or tardigrades and some other minute animalcules) the desiccation, or "drying-up" of the water in which they were living, swimming, and crawling (see Chapters XV. and XVI.). And it is quite probable that this power of resistance to the adverse conditions of changing seasons has, in the crawling Rotifers, taken the place of the production of eggs fertilized by a male. For, as in the case of the crustacean water-fleas (and of the terrestrial plant-lice, or aphides and gall-flies), it is found that the female Rotifers or wheel animalcules, which hatch from fertilized eggs, are themselves "parthenogenetic," and lay eggs which develop without fertilization by males—that is to say, are "impaternate." In the case of the water-fleas these are called "summer eggs," and after one or more generations of such fatherless females a proportion of males are produced which fertilize the females hatched at the same period. The eggs so fertilized acquire a thick shell and are called "winter eggs." They remain dormant for some months and resist the injurious influences of winter cold, or, it may be, of drying up and conversion of the pond-mud into dust, but hatch out when warmer and wetter conditions return.
This, however, is just what the adult crawling kind of Rotifer can do in the full-grown state by drawing up her body into the shape of a ball and exuding a jelly-like or horny coat. So that she has no need of "winter eggs," and the whole process of forming them and of males to impregnate them has "dropped out" of the life-history of this special kind of resistant Rotifers. The minute insignificant males and the eventual disappearance of males altogether in some races is a subject which may well occupy the attention of our human "suffragettes." That the males are minute creatures, less than the thousandth part of the size of the females, is a fact also ascertained in the case of some curious marine worms (called Bonellia and Hamingia). The only other instance of such degradation of the male sex is in some of the barnacles (discovered by Darwin), in which the big individuals are of double sex (hermaphrodite). Adhering to the shells of these are found minute dot-like "supplemental males." It is to be observed that these are instances where the inferiority of the male is an obvious measurable fact. In the mammals, the group of vertebrate animals to which man belongs, the male possesses measurably greater activity and size than does the female, and is provided with more powerful natural weapons, such as teeth and horns. He entirely dominates and controls the female, or a whole company of females, and in no case is there equality of the sexes, or any approach to it, still less inferiority of the male. It is, perhaps, a question whether "by taking thought" this natural inferiority of the mammalian female can be changed.
The survival of Rotifers, especially of a pink-coloured species (called Philodina roseola), after long drying or "desiccation," has been experimentally studied. It is found that if the water in which some are swimming is placed in a watch-glass and allowed to dry up rapidly the Rotifers are killed, none reappear when after a few hours fresh water is poured into the watch-glass. But if a few grains of sand or particles of moss are present from the first in the water the final drying up takes place more slowly and the Rotifers find their way between the sheltering fragments, where the water remains long enough to give them time to form a little gelatinous case, each for itself. When thus encased they survive, motionless, for months. The experiment has often been made, and is not in doubt. According to trustworthy statements, Philodina can thus survive even for so long as five years. The processes of life are arrested, but the drying has not proceeded to the extent which is called chemical drying or dehydration. The tiny Rotifers are still of soft consistence: the protoplasm is not chemically destroyed. When one is watched with the microscope as water is allowed to flow round it after several months of dust-like aridity, it is seen to emerge from its protective case and at once to commence swimming and searching for food by means of the currents directed towards its mouth by its so-called "wheel-apparatus." I may just say that in the case of the slime-mould called "flowers of tan" the protoplasm dries to the consistency of hard wax, and I have kept it for years in that state and then revived it by moisture into full activity and growth. I used also at one time to keep in my laboratory a supply of the dried yellow lichen from apple-trees, in which one could always rely upon finding the animalcules called "Macrobiotus" or "water-bears" ready to be revived from a desiccated condition, after three or four years passed in that condition.
Many of the Rotifers carry their eggs when ripe extruded from the body in two bunches or clusters, as is the habit also of the little microscopic shrimps known as Cyclops. There is a whole group of Rotifers which fix themselves by the tail, when full grown, to some solid support. Each then forms a protective tube or case around itself, from the mouth of which it puts forth its wheel-apparatus and into which it can retire for protection. Some of the largest and most beautiful of the wheel animalcules belong to this group of fixed or sedentary Rotifers. The crown animalcule (Stephanoceros) is one of these, having what are discs edged with vibrating hairs in the common Rotifer—here drawn out into a circlet of tapering lobes like the points of a coronet (Fig. 37 (bis), B). Another is the floscule (Floscularia), in which the wheel-apparatus has the form of five knobs arranged on a pentagonal disc around the mouth (A in same figure). Each knob has a bundle of excessively fine, long, stiff, motionless hairs spreading out from it ready to entangle food particles which may drift into contact with them. I used to find the stems of the fresh-water polyp (Cordylophora) of Victoria Dock a sure source of supply of these fine little creatures. When seen under the microscope as brightly illuminated glassy florets on a black ground (by what is called "dark ground illumination") their strange delicacy and beauty cannot be surpassed. A rare species of floscule (which I have never seen) has extra-long and fine filaments, each of which shows a fine streaming current in its substance, and is, in fact, a naked filament of living protoplasm like one of the ray-like filaments of the sun-animalcules.
Fig. 37 (bis).—Three tube-building wheel animalcules. A, Floscularia campanulata. B, Stephanoceros Eichhornii. C, Melicerta ringens.
The most curious of the tube-building Rotifers are those which form their tubes of little, equal-sized pellets of solid matter—as it were, "bricks"—which they first form by compacting fine particles in a special pit on the head and then build them up and cement them together in rows to form the tube, adding row after row as the animal itself increases in length (Fig. 37 (bis), C). These are known as Melicerta; and, though some kinds use any minute particles to make their bricks, one kind is frequent which uses its own excrement for this purpose. By feeding the little creatures first with food coloured with carmine and then with blue-stained material, one can obtain alternate rows of pink and blue pellets, carefully manufactured and laid in position to build up the growing length of tube. Melicerta has certainly an extraordinary and economical way of disposing of that refuse which we larger creatures carefully remove from our habitations and should be very unwilling to employ as building material. The individuals of one rare and interesting kind of the tube-builders, after swimming freely in the youngest stage, settle down together and form their gelatinous transparent tubes side by side, to the number of fifty or more, in such a way as to produce a perfect sphere, a twentieth of an inch or more in diameter, built up of fused jelly-like tubes radiating from a common centre. The inhabitant of each tube is quite separate from and independent of his neighbours, but they all protrude their vibrating wheel-apparatus simultaneously, and cause the glass-like ball to rotate and travel through the water. Many years ago I found this beautiful little thing in a small moss-pool (not more than 3 ft. wide), high up the sloping-side of the north-west section of Hampstead heath, above the "Leg of Mutton Pond." The well-meant care of the public guardians of the heath has now drained this region, and my little moss-pools and the "bog," in which grew the Drosera, or Sun-dew, and the Bog-bean and such plants, have gone for ever. But we must console ourselves with the fact that the same progressive expansion of the great city has given us electric railways, tubes, and tramways by which we can go farther afield than Hampstead in a few minutes, and still find moss-pools and the undisturbed glories of ancient swamps and bog-land.
Many of the Rotifers have a pair of ruby-red eyes, and in some of them there is a minute crystalline lens overlying the red sensitive spot, which receives the fibres of the optic nerve coming from the brain—one on each side. It is almost incredible that so minute a creature—often only the one-fiftieth of an inch long when full grown—should have a nervous system and special organs of touch (sensory hairs) as well as eyes, and on the other hand muscles running from one attachment to another and called into activity by nerves connected with this same central brain. The pair of branched tubes, which end internally in flickering "flame-cells" and open externally far back at the vent, are kidneys. Similar tubes called "nephridia" or little kidneys are found in many of the smaller animals; the earthworm has a pair in each ring of its body.
There is little doubt that the wheel animalcules are related in pedigree to the primitive ancestors of the marine segmented or annulate worms, which also gave rise to the ringed leg-bearing jaw-footed creatures with hard skin, called Crustacea, Arachnids and Insects (the Arthropods). The wheel-apparatus or cilia-fringed discs of the Rotifer is seen in the young stages of many marine worms, and also in the young of marine snails, known as the "veliger"—"velum" or "sail" being the name given to the wheel-apparatus of the young snails (see the drawing on p. 181). There are very minute marine annulate or segmented worms (Dinophilus and others), which come near to the Rotifers in many features, whilst the ringed or segmented character of the body is obvious in the common wheel animalcule.
The Rotifers are so small that they are built up of very few "cells" or nucleated units of protoplasm. Many of them are of smaller size than some of the big infusorian animalcules, which consist of a single cell. The Rotifers are probably a dwindled pygmy race descended from ancestors of ten or a hundred times their linear measurement. It is an important fact that in the possession of a toothed gizzard, in the hard body-case or cuirass of some kinds, and in Pedalion's rapidly-moving legs or paddles, fringed with plumose hairs and moved by that peculiar variety of muscular tissue which is called "striped muscular tissue," the wheel animalcules give evidence of relationship to the Crustacea—that is to say, it appears to be probable that they were derived from the common ancestor of marine worms and Crustacea before those two lines of descent had diverged.
Rotifera or wheel animalcules are found all over the world, in the tropics, the temperate zones, the Arctic and Antarctic, and many species have a world-wide distribution. They occur in fresh waters and in the sea, in great lakes, in gutters which dry up, in pools in the polar regions and on high mountains which are solid ice for the greater part of the year. A few are parasitic, some living on the legs of minute Crustacea. One which I discovered in 1868 in the Channel Islands lives in crowds on the skin of a remarkable sea-worm (Synapta), which burrows in the sand, exposed at low tide. It holds on (as I found and figured) by a true sucker, which replaces the forked tail of other commoner Rotifers. It was named "Discopus" by Zelinka, who searched for it in consequence of my description, and gave a very detailed account of it. Others are parasitic inside earthworms, and one is found inside the globe animalcule Volvox! Another causes the growth of warts or "galls" in a curious kind of Alga called Vaucheria.
CHAPTER XV
SUSPENDED ANIMATION
OUR leading newspapers, with rare exceptions, never report the discoveries announced at our scientific societies. But they often seek to astonish their readers with silly stories of monsters said to have been seen in tropical forests, ghostly "manifestations" and such rubbish transmitted to them at a high price by crafty "newsmongers," and do much harm to themselves and to the public thereby. On the other hand, foreign newspapers do occasionally report the proceedings of their local Academies—and then "our own correspondent" telegraphs to London with a flourish, a confused report of what he has read and ignorantly imagines to be "a startling discovery" because he knows nothing whatever of the subject. Thus shortly before the recent war—the confirmation by a French experimenter of the fact, long since demonstrated, that the seeds of plants can survive exposure to very low temperature, was announced with ridiculous emphasis by one of these "fat boys" of journalism pour épater le bourgeois.
A temperature very near to that of the total absence of that molecular movement or vibration which we call "heat," can now be attained by the use of liquid hydrogen, which enables us, by its evaporation, to come within a few degrees (actually three!) of that condition known as the "absolute zero." We divide into one hundred equal steps or degrees the column of liquid (mercury, spirit, or other liquid) of a thermometer as it expands from the shrunken bulk which it occupies when placed in freezing water to the full length which it attains when the water is heated to boiling point. This is called the centigrade scale, or scale of a hundred degrees. But, as we know by the records of travellers in the Arctic regions and by the experiments made in laboratories, there are "degrees" of coldness or diminution of heat which are much below that of freezing water, and can be measured by the further shrinking of the column of liquid in the thermometer, so that we record "degrees below zero centigrade," each of the same length as those above it and corresponding to the same "quantum" of decrease or increment of heat. As we pass from the temperature at which water is solid to that much lower or diminished state of hotness at which mercury becomes solid, the shrinking column of the thermometer (in which a liquid is used not rendered solid by this amount of cooling) falls through 39 degrees of the centigrade size, so that we say that mercury freezes at minus 39 or at 39 degrees below zero of the centigrade scale. The conclusion has now been reached that the absolute zero or cessation of all heat in a body is represented by a fall of no less than 273 degrees below zero on the centigrade scale. Hydrogen gas becomes a liquid at 252 degrees below zero centigrade, and a solid at 264 degrees. If we start our counting of those degrees or increments of heat, of which there are 100 between the freezing and boiling points of water, at the absolute zero or condition of total absence of heat, we must say that hydrogen "melts"—that is, passes from the solid to the liquid state—at 11 degrees (absolute), and boils at about 20 degrees (absolute), whilst water does not melt until 273 degrees (absolute) of temperature are reached, and boils at 373 degrees above the absolute zero.
It is the fact that, from the year 1860 onward, numerous observers have experimented on the influence of very low temperatures upon seeds, and have uniformly shown that the power of germination and healthy growth of the seeds is not destroyed by exposure to very low temperatures. The celebrated Swiss botanist, De Candolle, published the first careful observations on this subject in conjunction with Raoul Pictet, who had devised an apparatus for producing exceedingly low temperatures. Pictet in 1893 exposed various bacteria and also seeds to a temperature of nearly 200 degrees below zero centigrade without injury to them. They "resumed" their life when gradually restored to the normal temperature. Pictet concluded that since all chemical action of the kind which goes on in living things requires a certain degree of temperature for its occurrence, and that this is demonstrably considerably higher than minus 100 degrees centigrade, we must suppose that all chemical action in living things (as in nearly all other bodies) is annihilated at 100 degrees below zero centigrade. Accordingly he maintained that what we call "life," or "living," is a manifestation of chemical forces similar to those shown in other natural bodies, and liable to interruption and resumption by the operation of unfavourable or favourable conditions as are other chemical processes. In 1897, Mr. Horace Brown and Mr. F. Escombe published, in the Proceedings of the Royal Society of London, an account of experiments in which they exposed seeds of twelve plants belonging to widely different natural orders to a temperature varying from 183 degrees to 192 degrees below zero centigrade for a period of 110 consecutive hours (about four days and a half). As a result the germinative powers of the seeds showed no appreciable difference from that of seed not subjected to cold, and they produced healthy plants. The low temperature was obtained by the use of liquid air in a vacuum-jacketed flask (like the well-known "thermos" flasks), into which the seeds were introduced in thin glass tubes. Professor M'Kendrick had previously shown that the putrescence of meat, blood and milk by bacteria infesting them was temporarily arrested, but not permanently so, by exposing those substances for one hour to a temperature of 182 degrees below zero centigrade. It appeared that the putrefactive bacteria present in those substances were not destroyed by that degree of cold, but returned to a state of activity when the normal temperature was restored. Professor M'Kendrick also showed that seeds would germinate after exposure to like treatment.
All this is ancient history, twenty years and more in the past. The experiments of a French observer, mentioned at the beginning of this chapter as foolishly trumpeted in a London paper, were of service as confirming the extensive and careful work of his predecessors. It is only when our old well-bottled discoveries have, however tardily, been brought before the Paris Academy of Sciences and sent back to us by the Paris correspondents of news agencies as "startling novelties" and "amazing discoveries" (twenty years old), that any attempt is made to mention them in the London daily Press. And then they are announced without any reference to their true history. This habit of culling stale morsels of information from the proceedings of foreign academies points to the fact that there is incompetence both in the purveyor and publisher of such scraps. If our newspaper editors must publish scraps about scientific novelties, they should employ educated assistants to see that they do not make themselves ridiculous. The scraps which come round to our newspapers from Paris are usually plagiarized from a French newspaper by some one who has a very imperfect knowledge of the subject to which they refer, and adds his own blunders to those of the original reporter.
The action of extreme cold in arresting life in such minute organisms as plant seeds and bacteria without destroying the possibility of the resumption of those chemical and physical changes when warmth is restored, is dependent on the fact that those chemical changes can only proceed in and by the aid of liquid water. When thoroughly frozen the chemical constituents of minute organisms and seeds—which until frozen were living and undergoing continuous, though perhaps slow, change—become solid, and can no longer act on one another or be acted on by surrounding chemical bodies equally reduced in temperature. They may be compared to the solid dry constituents of a Seidlitz powder—one an acid, the other a carbonate. So long as they are dry they remain—when mixed and shaken together—inert, without action on one another. Even if one is dissolved in water and then frozen solid and mixed in a powdered state with the other at an equally low temperature the mixture remains dry and inert. Nothing happens so long as the low temperature is maintained. But if we raise the temperature above the freezing-point—so as to liquefy the solution—chemical action will immediately ensue. With much fizzing and escape of gas the two chemicals will unite. The effect of cold on living matter is of this nature. It is a real "suspension" of the changes which were—however slowly and quietly—going on before complete solidification of the protoplasm by freezing. A frozen seed and frozen bacteria are in a state of "suspended animation."
It is not the fact that absolutely all chemical union and change whatsoever is prevented—that is to say, arrested or suspended—by extreme cold, although the union with oxygen and other such changes of the essential material of living things, which we call "protoplasm," and most other chemical changes are thus arrested or suspended. The most striking exception is that of the most active of all elements, the gas fluorine, which becomes a liquid at 210 degrees below zero centigrade, and in that condition attacks turpentine if brought into contact with it at the same low temperature with explosive force. Even solid fluorine combines with liquid hydrogen with violent explosion. It seems certain, however, that elements or chemical compounds brought into the solid (not merely liquid) condition by extreme cold cannot act chemically upon other bodies in the same solid condition, even when they would at normal temperatures so act with the greatest readiness, because they are then either liquid or gaseous.
The conception of an arrest of the changes in organisms, which we call life, followed by their resumption after a greater or less interval of suspense, was long ago suggested and discussed before we had knowledge of the action of low temperatures. The winter-sleep of some animals and the "comatose" condition sometimes exhibited by human beings had led to the notion of "suspended animation." But a careful study of hybernating animals and of human instances of prolonged "coma" satisfied physiologists nearly 100 years ago that the processes of life—the beating of the heart and the respiration—were not actually and absolutely suspended in these cases, but reduced to a minimum. The chemical processes connected with life were still very slowly carried on.
Again, a great deal of interest and discussion was excited in the last century by the drying up of delicate yet complex aquatic animalcules, such as the Rotifers (the wheel animalcules described in our last chapter) and Tardigrades (bear animalcules), and the fact that after their preservation as mere dust for many months dried on a glass-slip they could be revived and made to return to life by wetting them with a minute drop of water, whilst the whole process of revival was watched under the microscope. Letters were published in the "Times" in the "fifties" by the Rev. Lord Sydney Godolphin Osborn, describing his observations and experiments on these animalcules.
The yellow slime-fungus called "flowers of tan," after creeping as a naked network of protoplasm over the "spent tan," thrown out from tan-pits, will in dry weather gather itself into little knobs, each of which is as hard and brittle as a piece of sealing-wax. Yet (as I have repeatedly experienced in using material given to me by the great botanist, de Bary) a fragment of one of these hard pieces, if carefully guarded in a dry pill-box for two or three years, will when placed on a film of water at summer-heat gradually absorb moisture and expand itself into threads of creeping, flowing protoplasm, nourish itself, and grow and reproduce. It was formerly suggested in regard to these cases of resuscitation after drying, as also in the case of seeds which germinate after being kept in a dry condition for many years, that really they were not thoroughly dried, but were sufficiently moist to allow of very slow oxidation and gas exchange, which it was said was so small in amount as to escape observation. There was a plausible comparison of the condition of these dried organisms to that of hybernating mammals, desiccated snails, and comatose men. It was held that here, too, the life-processes were not absolutely arrested, but reduced to an imperceptible minimum.
This view of the matter was connected, no doubt, with a traditional assumption that life was an entity—an "anima animans"—which entered a living body, kept it continually "going" or "living," and if driven out from it could not return. Curiously enough, Mr. Herbert Spencer seems to have been (perhaps unconsciously) affected by this traditional view, since he defined life as "the continuous"—that is the important word—"adaptation of internal to external relations." This definition prejudiced the view of some distinguished physiologists on the question of "suspended animation," and I remember a very warm dinner-table discussion with Michael Foster and other friends, some twenty-five years ago, when I put forward the view that so long as the intimate structure—in fact, the chemical structure—of the protoplasm of a living thing is not destroyed, it does not "die" though all chemical change in it may be arrested. I compared the dried seed and dried animalcule—as I would now compare the frozen seed and the frozen bacteria—to a well wound watch which is stopped by the intrusion of a needle between the spokes of its balance wheel, or, better, by the cooling on the wheel of a tiny drop of soft wax so as to clog it. The works of the watch are rendered absolutely motionless, but it is not "dead." As soon as the needle is removed or the tiny speck of wax melted by a gentle warmth it resumes its movement. It is, as we say, "alive again." So, too, the frozen or dried organism is absolutely motionless. No chemical movements can go on in it. They are stopped by the solidity set up by freezing, or in the case of simple "desiccation," by the absence of the moisture necessary for bringing the chemical molecules into contact. If protected from destructive agents, the mechanism remains perfect for just so many years or centuries as that protection lasts. Whenever the frozen organism thaws or the dried organism becomes wet, the life-processes are resumed, the seed germinates, the bacteria grow and multiply.
Thus we see what are some of the points of interest and importance raised by the old experiments of Pictet, M'Kendrick, and Horace Brown, the results of which were the same as those announced as Parisian novelties. I have yet to say a few words as to the reason why we cannot produce "suspended animation" in higher organisms or in man by the application to them of extreme cold. Further, the influence of extreme cold on the possible passage, through space, of living germs from other worlds to this earth—a possibility suggested by the late Lord Kelvin—requires some consideration in connection with the striking experiments with phosphorescent bacteria described ten years ago by Sir James Dewar.
Young stages of growth or Veliger larvæ of marine snails, showing the ciliated band or velum which is identical with the wheel apparatus of the Rotifers or Wheel animalcules.
CHAPTER XVI
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.