cellular germ, the name of "germinal matter," and to all the other substance entering into the composition of tissue, being secondary, and produced the name of "formed matter."

"Wherever there is life there is protoplasm; wherever there is protoplasm, there, too, is life." The physical consistence of protoplasm varies with the amount of water with which it is combined, from the solid form in which we find it in the dormant state to the thin watery state in which it occurs in the leaves of valisneria.

As to its composition, chemistry can as yet give but scanty information; it can tell that it is composed of carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorus, and it can also tell the percentage of each element, but it cannot give more than a formula that will express it as a whole, giving no information as to the nature of the numerous albuminoid substances which compose it. Edward Cope, in his article on Comparative Anatomy,[5] gives the formula for protoplasm (as a whole), C₂₄H₁₇N₃O₈ + S and P, in small quantities under some circumstances. It is therefore, he says, a nitryl of cellulose: C₂₄H₂₀O₂ + 3NH₃. According to Mulder the composition of albumen, one of the class of protein substances to which protoplasm belongs, is 10(C₄₀H₃₁N₅O₁₂) + S₂P. Protoplasm is identical in both the animal and vegetable kingdom; it behaves the same from whatever source it may be derived towards several re-agents, as also electricity. Is it possible, then, that the protoplasm which produces the mould is exactly the same composition as that which produces the human child? The answer is Yes, so far as the elements are concerned, but the proportions of carbon, hydrogen, etc., must enter into an infinite number of diverse stratifications and combination in the production of the various forms of life. Professor Frankland, speaking of protein, for instance, says it is capable of existing under probably at least a thousand isomeric forms. Protoplasm may be distinguished under the microscope from other members of the class to which it belongs, on account of the faculty it possesses of combining with certain coloring matters, as carmine and aniline; it is colored dark-red or yellowish-brown by iodine and nitric acid, and it is coagulated by alcohol and mineral acids as well as by heat. It possesses the quality of absorbing water in various quantities, which renders it sometimes extremely soft and nearly liquid, and sometimes hard and firm like leather. Its prominent physical properties are excitability and contractility, which Kühne and others have especially investigated. The motion of protoplasm in plants was first made known by Bonaventure Corti a century ago in the Charœ plants; but this important fact was forgotten, and it had to be discovered by Treviranus in 1807. The regular motion of the protoplasm, forming a perfect current, may be seen in the hairs of the nettle, and weighty evidence exists that similar currents occur in all young vegetable cells. "If such be the case," says Huxley, "the wonderful noonday silence of a tropical forest is, after all, due only to the dullness of our hearing, and could our ears catch the murmur of these tiny maelstroms, as they whirl in innumerable myriads of living cells, which constitute each tree, we should be stunned as with a roar of a great city."

One step higher in the scale of life than the monera is the vegetable or animal cell, which arose out of the monera by the important process of segregation in their homogeneous viscid bodies, the differentiation of an inner kernel from the surrounding plasma. By this means the great progress from a simple cytod (without kernel) into a real cell (with kernel) was accomplished. Some of these cells at an early stage encased themselves by secreting a hardened membrane; they formed the first vegetable cells, while others remaining naked developed into the first aggregate of animal cells. The vegetable cell has usually two concentric coverings—cell-wall and primordial utricle. In animal cells the former is wanting, the membrane representing the utricle. As a general fact, also, animal cells are smaller than vegetable cells. Their size[6] varies greatly, but are generally invisible to the naked eye, ranging from ¹⁄500 to ¹⁄10000 of an inch in diameter. About four thousand of the smallest would be required to cover the dot put over the letter i in writing. The shape of cells varies greatly; the normal form, though, is spheroidal as in the cells of fat, but they often become[7] many-sided—sometimes flattened as in the cuticle, and sometimes elongated into a simple filament as in fibrous tissue or muscular fibre.

The cell, therefore, is extremely interesting, since all animal and vegetable structure is but the multiplication of the cell as a unit, and the whole life of the plant or animal is that of the cells which compose them, and in them or by them all its vital processes are carried on. It may sound paradoxical to speak of an animal or plant being composed of millions of cells; but beyond the momentary shock of the paradox no harm is done.

The cell, then, can be regarded as the basis of our physiological idea of the elementary organism; but in the animal as well as in the plant, neither cell-wall nor nucleus is an essential constituent of the cell, inasmuch as bodies which are unquestionably the equivalents of cells—true morphological units—may be mere masses of protoplasm, devoid alike of cell-wall or nucleus. For the whole living world, then, the primary and a mental form of life is merely an individual mass of protoplasm in which no further structure is discernible. Well, then, has protoplasm been called the "universal concomitant of every phenomena of life." Life is inseparable from this substance, but is dormant unless excited by some external stimulant, such as heat, light, electricity, food, water, and oxygen.

Although we have seen that the life of the plant as well as of the animal is protoplasm, and that the protoplasm of the plant and that of the animal bear the closest resemblance, yet plants can manufacture protoplasm out of mineral compounds, whereas animals are obliged to procure it ready made, and hence in the end depend on plants. "Without plants," says Professor Orton, "animals would perish; without animals, plants had no need to be." The food of a plant is a matter whose energy is all expended—is a fallen weight. But the plant organism receives it, exposes it to the sun's rays, and in a way mysterious to us converts the actual energy of the sunlight into potential energy within it. It is for this reason that life has been termed "bottled-sunshine."

The principal food of the plant consists of carbon united with oxygen to form carbonic acid, hydrogen united with oxygen to form water, and nitrogen united with hydrogen to form ammonia. These elements thus united, which in themselves are perfectly lifeless, the plant is able to convert into living protoplasm. "Plants are," says Huxley, "the accumulators of the power which animals distribute and disperse." Boussengault found long