dust particles mixed with the dried mud of a drop of dirty water. They may be kept in this state for months -even years. I do not know that any limit has been ascertained. But when you add pure rain-water to the dust in the watchglass, it softens, and in less than an hour the little wheel-animalcules have softened too, and expanded into life, swimming about whilst the delicate spikes on their "wheels" vibrate regularly as though they had never ceased to do so, and as though the animalcules had not for years been dried-up little mummies,

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

WITH

THINGS

ITHOUT 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.

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 th to th 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

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 amoeba; 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 "amoeboid," from its resemblance to the amoeba 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 amoeba, 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 amoeba'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.

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

FIG. 37.-A, cells forming soft vegetable tissue; a, cell-wall; b, protoplasm; c, liquid-holding cavity in the protoplasm; d, the nucleus. B, a pigment-cell from the frog's skin, expanded. C, the same cell contracted. D, a nerve-cell: observe the nucleus. E, a musclecell stretched. F, the same contracted: observe the nucleus.

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.

How did these viscous nucleated corpuscles come to be called "cells"? It was in this wise. At the end of the seventeenth century Dr. Robert Hook, secretary of

the Royal Society, published a beautiful book of folio size, entitled Micrographia. In this he pictured various minute insects and various natural products as seen under his microscope. Among the objects figured and described was a piece of cork (Fig. 38). Hook showed that it was built up of a number of empty, air-holding, box-like chambers, less than the hundredth of an inch in length, and these he called "cells," comparing them to the "cells" of the bee's honeycomb. Later observers

FIG. 38.-Copy of part of Robert Hook's drawing of a magnified
piece of cork, showing the "cells" so named by him in 1665.

found that this "cellular" structure was very common in plants-but it was not until more than a hundred years later that it was observed that the "cells" which build up the soft stems and leaves of plants are not empty or merely air-holding, but contain a liquid or viscid matter. Robert Browne, a great botanist, who lived within the memory of some of our older naturalists, first observed and described the "nucleus," or kernel, within the cells of some lily-like plants, and gave it that name (Fig 37 A, d). About the thirties of last century, by aid of improved