for any reason or for any necessity that lies in the nature of the case, but simply for the habit of the thing-has not yet put himself at home with the metaphysical categories of substance and casualty; thanks, perhaps, to those guides of his whom we, the amusing Britons that we are, bravely proclaim "the foremost thinkers of the day"!

The matter and manner of the whole essay are now fairly before us, and I think that, with the approbation of the reader, its procedure, generally, may be described as an attempt to establish, not by any complete and systematic induction, but by a variety of partial and illustrative assertions, two propositions. Of these propositions the first is, That all animal and vegetable organisms are essentially alike in power, in form, and in substance; and the second, That all vital and intellectual functions are the properties of the molecular disposition and changes of the material basis (protoplasm) of which the various animals and vegetables consist. In both propositions, the agent of proof is this same alleged material basis of life, or protoplasm. For the first of them, all animal and vegetable organisms shall be identified in protoplasm; and for the second, a simple chemical analogy shall assign intellect and vitality to the molecular constituents of the protoplasm, in connection with which they are at least exhibited.

In order, then, to obtain a footing on the ground offered us, the first question we naturally put is, What is Protoplasm? And an answer to this question can be obtained only by a reference to the historical progress of the physiological cell theory.

That theory may be said to have wholly grown up

since John Hunter wrote his celebrated work 'On the Nature of the Blood,' etc. New growths, to Hunter, depended on an exudation of the plasma of the blood, in which, by virtue of its own plasticity, vessels formed, and conditioned the further progress. The influence of these ideas seems to have still acted, even after a conception of the cell was arrived at. For starting element, Schleiden 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. It was then that, in this connection, we heard of the terms blastema and cyto-blastema. The theory of the vegetable cell was completed earlier than that of the animal Completion of this latter, again, seems to have been first effected by Schwann, after Müller had insisted on the analogy between animal and vegetable tissue, and Valentin had demonstrated a nucleus in the animal cell, as previously Brown in the vegetable one. But assuming Schwann's labor, and what surrounded it, to have been a first stage, the wonderful ability of Virchow may be said to have raised the theory of the cell fully to a second stage. Now, of this second stage, it is the dissolution or resolution that has led to the emergence of the word Protoplasm.

one.

The body, to Virchow, 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, further, propagated themselves, chiefly by partition or division; and the fundamental principle of the whole

theory was expressed in the dictum, "Omnis cellula e cellula." That is, the nucleus, becoming gradually elongated, at last parted in the midst; and each half, acting as center of attraction to the surrounding intracellular matrix or contained matter, stood forth as a new nucleus to a new cell, formed by division at length of the original cell.

The first step taken in resolution of this theory was completed by Max Schultze, preceded by Leydig. This was the elimination of an investing membrane. Such membrane may, and does, ultimately form; but in the first instance, it appears, the cell is naked. The second step in the resolution belongs perhaps to Brücke, though preceded by Bergmann, and though Max Schultze, Kühne, Hæckel, and others ought to be mentioned in the same connection. This step was the elimination, or at least subordination, of the nucleus. The nucleus, we are to understand now, is 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? Why, nothing but what was the contained matter, the intracellular matrix, and is-Protoplasm.

In the application of this word itself, however, to the element in question, there are also a step or two to be noticed. The first step was Dujardin's discovery of sarcode; and the second the introduction of the term protoplasm as the name for the layer of the vegetable cell that lined the cellulose, and enclosed the nucleus. code, found in certain of the lower forms of life, was a simple substance that exhibited powers of spontaneous contraction and movement. Thus, processes of such simple, soft, contractile matter are protruded by the

Sar

rhizopods, and locomotion by their means effected. 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 prominence.

In this account I have necessarily omitted many subordinate and intervening steps in the successive establishment of the contractility, superior importance, and complete isolation of this thing to which, under the name of protoplasm, Mr. Huxley of late has called such vast attention. Besides the names mentioned, there are others of great eminence in this connection, such as Meyen, Siebold, Reichert, Ecker, Henle, and Kölliker among the Germans; and among ourselves, Beale and Huxley himself. John Goodsir will be mentioned again.

We have now, perhaps, obtained a general idea of protoplasm. Brücke, when he talks of it as "living cell-body or elementary organism," comes very near the leading idea of Mr. Huxley as expressed in his phrase, "the physiological basis, or matter, of life." Living cell-body, elementary organism, primitive living matter -that, evidently, is the quest of Mr. Huxley. There is aqueous matter, he would say, perhaps, composed of hydrogen and oxygen, and it is the same thing whether in the rain-drop or the ocean; so, similarly, there is vital matter, which, composed of carbon, hydrogen, oxygen, and nitrogen, is the same thing whether in cryptogams or in elephants, in animalcules or in men. What,

in fact, Mr. Huxley seeks, probably, is living proteinprotein, so to speak, struck into life. Just such appears to him to be the nature of protoplasm, and in it he believes himself to possess at last a living clay wherewith to build the whole organic world.

The question, What is Protoplasm? is answered, then; but, for the understanding of what is to follow, there is still one general consideration to be premised..

Mr. Huxley's conception of protoplasm, as we have seen, is that of living matter, living protein; what we may call, perhaps, elementary life-stuff. Now, is it quite certain that Mr. Huxley is correct in this conception? Are we to understand, for example, that cells have now definitively vanished, and left in their place only a uniform and universal matter of quite indefinite proportions? No; such an understanding would be quite wrong. Whatever may be the opinion of the adherents of the molecular theory of generation, it is certain that all the great German histologists still hold by the cell, and can hardly open their mouths without mention of it. I do not allude here to any special adherents of either nucleus or membrane, but to the most advanced innovators in both respects; to such men as Schultze and Brücke and Kühne. These, as we have seen, pretty well confine their attention, like Mr. Huxley, to the protoplasm. But they do not the less on that account talk of the cell. For them, it is only in cells that protoplasm exists. To their view, we cannot fancy protoplasm as so much matter in a pot, in an ointment-box, any portion of which scooped out in an earpicker would be so much life-stuff, and, though a part, quite as good as the whole. This seems to be Mr. Huxley's conception, but it is not theirs. A certain