vessels formed, and conditioned the further progress. When, at a later date, the conception of a cell had been arrived at, Schleiden, for starting point, required an intracellular plasma, and Schwann, a structureless exudation, in which minute granules, if not indeed already pre-existent, formed, and by aggregation grew into nuclei, round which singly the production of a membrane at length enclosed a cell. Brown demonstrated a nucleus in the vegetable cell; as Valentin subsequently did in the animal one; Müller insisted on the analogy between animal and vegetable tissue; Schwann's labour in completing the theory of the animal cell may be regarded as completing the first stage of the cell theory: but the raising it to the second stage must be attributed to the wonderful ability of Virchow. And it is to the resolution of this second stage that we owe the word Protoplasm.

In Virchow's view, the body constituted a free state of individual subjects, with equal rights but unequal capacities. These were the cells, which consisted each of an enclosing membrane, and an enclosed nucleus with surrounding intracellular matrix or matter. These cells propagated themselves, chiefly by partition or division; and the fundamental principle of

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the entire theory was expressed in the dictum, "Omnis cellula e cellula."

The first step in resolution of this theory was the elimination of the investing membrane. Such membrane may and does ultimately form ; but in the first instance, for the most part, the cell is naked. The second step was the elimination, or at least the subordination, of the nucleus. The nucleus is now discovered to be necessary neither to the division nor to the existence of the cell.

Thus, then, stripped of its membrane, relieved of its nucleus, what now remains for the cell? Nothing, but that which was the contained. matter, the intracellular matrix, and is-Protoplasm.

The application of the word, however, to the element in question, like the history of the thing, was marked by several stages. First came Dujardin's discovery of sarcode. Then, as above mentioned, Von Mohl's introduction of the term protoplasm as the name for the layer of the vegetable cell that lined the cellulose, and enclosed the nucleus. Cohn, four years later, proclaimed "the protoplasm of the botanist, and the contractile substance and sarcode of the zoologist" to be, "if not identical, yet in a high degree analogous substances."

Remak first extended the use of the term protoplasm from the layer which bore that name in the vegetable cell to the analogous element in the animal cell; but "it was Max Schultze, in particular, who by applying the name to the intracellular matrix, or contained matter, when divested of membrane, and by identifying this substance itself with sarcode, first fairly established protoplasm, name and thing, in its present position."

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In England, however, it is Professor Huxley who, by his brilliant and well-known Essay on this subject in the Fortnightly Review for February, 1869, has acquired a prominence, though by no means a pre-eminence, all his own. ing for his theme the "Physical Basis of Life," and treading in the track of that "host of investigators" of whom he tells us that they "have accumulated evidence, morphological, physiological, and chemical," in favour of that “immense unité de composition élémentaire dans tous les corps vivants de la nature," of which Payen wrote so clearly nearly thirty-five years ago; he combats "the widely-spread conception of life as a something which works through matter, but is independent of it"; and affirms, on the contrary, "that matter and life are inseparably connected, and that there is

one kind of matter which is common to all living beings."

Notwithstanding the wide diversity that presents itself to our view in the countless varieties of living beings, it yet is true that all vegetable and animal tissues without exception, from that of the brightly coloured lichen on the rock, to that of the painter who admires or of the botanist who dissects it, are essentially one in composition and in structure. The microscopic fungi clustering by millions within the body of a single fly, the giant pine of California towering to the height of a cathedral spire, the Indian fig-tree covering acres with its profound shadow, animalcules minute enough to dance in myriads on the point of a needle, and the huge leviathan of the deep, the flower that a girl wears in her hair, and the blood that courses through her veins, are, each and all, smaller or larger multiples or aggregates of one and the same structural unit, and all therefore ultimately resolvable into the same identical elements. That unit is a corpuscle composed of oxygen, hydrogen, nitrogen, and carbon. Hydrogen, with oxygen, forms water; carbon, with oxygen, carbonic acid; and hydrogen, with nitrogen, ammonia, These three compounds-water, carbonic acid, and ammonia,-in like manner, when combined form protoplasm.

In all this, however, there is nothing new but the nomenclature. 1 But the case is widely altered when Mr. Huxley proceeds to assert that amid all the diversities of living things and living beings there exists a threefold unity: a unity of faculty, a unity of form, and a unity of substance. In relation to the first of these, for example, faculty, power, activity; according to Mr. Huxley, even human activities must be referred to three categories-contractility, alimentation, and reproduction; and for the lower forms of life, whether animal or vegetable, there are no fewer than these same three. The granulated, semi-fluid layer which constitutes the lining of the woody case of the nettle-sting is possessed of contractility. And in this possession of contractile substance, other plants are as the nettle, and all animals are as plants. Protoplasm is common to the whole of them; and this lining in the sting of the nettle is protoplasm. So that between the powers of the lowest plant or animal and those of the highest, the difference is one not of kind, but only of degree. The colourless blood-corpuscles in

1 And this nomenclature, though new, is by no means improved. It is inexact, indefinite, indiscriminate, and therefore necessarily misleading. See below; especially pages 132, 135-142.