Of course, the term “suspended animation” has been applied in earlier times to the often exaggerated stories of “trance” and deathlike sleep in human beings. But it is now with more justice applied to these instances of dried animalcules which return to life when wetted, and to similar cases of prolonged retention of vitality by seeds, since it would appear that in these dried animalcules life really is actually and totally suspended, although the mechanism is there which resumes its life when the necessary moisture is supplied. In cases of trance in man and hibernation in animals, the heart is still very slowly and feebly beating, and the breathing is still—almost imperceptibly—at work. The chemical changes are still very slowly and gently proceeding. The buried Indian wizard, and the snail, and the Sleeping Beauty are moist, and chemically active, though feebly so; life is not absolutely suspended. But in the dried animalcule (though complete chemical desiccation is not effected), the removal of the water from the body actually arrests the changes which we call life, just as a needle may arrest the balance-wheel of a watch. Supply the water, or remove the needle, and life ceases to be suspended; it goes on once more (as one of the rules of Bridge ambiguously enacts) “as though no mistake had been made.”
[XVIII]
THE UNIVERSAL STRUCTURE OF LIVING THINGS
Without doubt, the greatest and most important statement which can be made about living things is that they are either separate minute particles of living matter or (more commonly) are built up by thousands of such minute particles which have in each individual animal and plant originated from a single such particle (the fertilised germ), by its division into two, and the subsequent division of these two each into two, and of the four so produced each into two—and so on, until by repeated division into two, millions of corpuscles, hanging together as one mass, are the result.
Fig. 36.—Simple “cells,” consisting of naked protoplasm, changing shape and taking in solid food particles. A, is a series of four successive changes of shape of a fresh-water animalcule, the proteus or amœba; B, is a similar series of three views of a separate creeping kind of corpuscle found in the blood and lymph-spaces of animals, and called a “phagocyte.” It is also said to be “amœboid,” from its resemblance to the amœba or proteus-animalcule. B, is from the blood of the guinea-pig. It is not a parasite, but one of the various kinds of cells which build up the animal body, and are derived from the single original egg-cell (see [Fig. 31]) by continued division. The three drawings show three changes of shape occurring in the same “phagocyte” in a few minutes. It is engulphing a fever-producing blood-parasite, a spirillum, marked a, into its soft, slimy protoplasm, to be there digested and destroyed. In the same way the amœba, A, is seen in four stages of engulphing the vegetable particle, a. In the fourth figure the letter b points to water taken into the amœba’s protoplasm with the food-particle a. In all the figures, c points to the “vacuole” or liquid-holding cavity, which bursts and re-forms in A; the letter d points to the cell-nucleus.
The particles of living matter are spoken of as “cells” for a very curious reason, to which I will revert. The living matter is called “protoplasm” (primitive or fundamental slime). A “cell” in the language of microscopists means a corpuscle or more or less rounded or irregularly shaped particle of protoplasm. Cells commonly vary in size from 1/5000th to 1/200th of an inch in breadth, and may be much larger. Protoplasm—the living substance of “cells”—is a slimy body, almost liquid, but yet tenacious. It is transparent, but clouded by fine granules, and can often be seen with a very high power of the microscope to consist of more and of less liquid matter, intermixed like an emulsion. It often has within it large cavities filled with liquid, and also often oil drops; in other cases hard concretions or coarse granules. But apart from other things, the protoplasm of a “cell” always contains within it a special, firmer, and denser part, enclosed in an enveloping coat or skin. This dense body is the “nucleus,” or kernel, and is of the very greatest importance in the chemical changes and movements which constitute the life of the cell. It is usually spherical, and in the living state often looks clear and bright. All cells, whether they are found building up the bodies of plants and animals like so many living bricks, or living freely and singly as animalcules, have the essential structure just described—a semi-liquid yet tenacious material enclosing a globular firmer body, the nucleus.