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.