living thing is made, or, so far as known, has been made or ever will be made;

26. When it divides itself, is preceded sometimes in that act by the division of its nucleus, and sometimes not;

27. May throw off a portion of itself without a nucleus, and develop a nucleus in the detached portion. 28. Forms nuclei and nucleoli, which appear to differ sexually, as it is only after the intermingling of these in certain cases that multiplication takes place;

29. Does not transform the nucleus, or nucleolus, directly into formed material;

30. Transforms it into ordinary bioplasm, and thus into formed material;

31: When recently dead, will take a carmine stain from the solution of carmine in ammonia, as formed material will not;

32. At its death is resolved into fibrine, albumen, fatty matter, and salts;

33. Forms thus the spontaneously coagulable substance on the diffusion of which through the body the rigidity of the frame after death depends;

34. Is in direct continuity with formed material while the latter is in process of formation.

Such is the most interesting, by far, of all the objects known to physical science.

Carmine staining, the great discovery of 1856 and 1860, must take place immediately after the death of the bioplasm, or it cannot be successfully executed. Many unskilful manipulators in the laboratory, and

amateurs without number, have endeavored to stain the tissue of plants and animals, and have waited too long after its death, and have failed. Sometimes, too, they have not rightly compounded the materials for their carmine solution, a distinct receipt for which you will find in Beale's work on the microscope. When the process of staining is performed soon after the death of a tissue, all germinal points or bioplasts in it come out with a red color; but the formed material is not stained at all.

[From this point on, Mr. Cook referred to large colored diagrams hung on the wall back of the platform.]

These eloquent representations of stained tissues are exact reproductions of Dr. Beale's famous illustrations, and were made by Mr. Stone, an artist of the Studio building, who spoke admiringly of Beale's illustrations the instant he saw them. Here is the whole cell with its wall, bioplast, and nucleus. (See plate I, fig. 1.) Two currents exist in every cell, — one flowing inward in the direction of this arrow, and the other passing out from the centre of the bioplast in the direction of this arrow. Every particle of matter that can be found in a living being is of one of three kinds, — nutrient matter, living matter, or formed matter. Nutrient matter comes through the wall of the cell, and, entering into the bioplasm, is there transformed into living matter.

You had better not take a cell, however, as the type of the elementary part in the living tissue. If you are to be abreast of the very latest investigations

concerning the cell-theory, you will take a naked mass of bioplasm like this as the elementary part. (See plate I, fig. 2.) As I showed you in my last lecture, on both Huxley's and Beale's authority, it is not essential at all that there be a wall of formed material around the naked mass of bioplasm. It is not essential at all there be a nucleus within it. That is the advance we have made since 1838. Nevertheless, if you are to understand the action of these currents, it is well to keep in mind the cellwall. Nutrient material may pass through the cellwall in animal tissues just as sap passes through the intercellular substance in vegetable tissues. When once in the bioplast, the nutrient matter is seized on by this living matter, which you see colored with carmine in all these illustrations, and nuclei are developed in the bioplast, and nucleoli within the nuclei. The bioplast produces the nucleus, and not the nucleus the bioplast. It throws off formed material around its quivering edges, and thus forms a cellwall. In that wall the oldest formed material is on the outside, and the next oldest just within, and so on to the inner part of the wall, which is in physical continuity with the bioplasm.

Movement is going on all the while in any naked mass of bioplasm. Here is a bioplast, naked, colorless, structureless matter; and it moves so that it takes these many shapes in five seconds, and these many other shapes in one minute. (See plate I, figs. 2 and 3.) Here we must hold fast to the Ariadne clew, that every change must have an

adequate cause. We come here to fathomless design; but let us enter by slow stages on these sublimities of research.

Here is a young tendon, and here is an old tendon. The living matter is red, as you notice, and runs in lines through the tendon; and yet the tendon is narrow. But in the old tendon the formed material is more abundant than in the new; and yet all the formed material which makes an increased thickness in the old has been thrown off by these bioplasts. They have here thrown off formed material 80 as to make a tendon, which is, as you know, a structure very different from muscular fibre and from nervous fibre.

Here is one set of bioplasts that is intended to weave a tendon, here one that is to weave a muscular fibre, and here one that is to weave a nervous fibre. There is no possible external influence that can make them exchange offices with each other. You have here a tendon, there a muscle, there a nerve, all woven by these bioplasts. We know that they are thus woven, and that every change must have an adequate cause. Adhere, gentlemen, to that axiomatic truth, though the heavens fall. From your bioplast spindles flows off formed matter- here a miracle of muscle, there a miracle of tendon, there a miracle of nerve.

The cellular integument is not unworthy of notice; for that shows us the career of its bioplasts from the first to the last. You have here the skin that covers one of the papilla on the tongue

of a frog. (See plate II, fig. 1.) That infinitely delicate membrane that covers the little sensitive points on the tongue is here magnified. You notice that the bioplasts on the lower or inner side are young, and that there is not much formed material around them. There are no distinct cells in the younger part of a tissue. This intercellular substance is not formed into the ring-shapes which you see further on, where the tissue is older. As the bioplasts grow, the formed material about them increases in thickness, until it becomes so thick that the nutrient matter will not go through the cell-walls. Then the bioplasts languish; they grow smaller and smaller, and at last the cells in which the bioplasts are dead scale off. When dead never before, except by violence—they drop away; but their places are supplied by soldiers that take position in the gap of the lines, and build according to the pattern of the design of the whole organization. You have here (see plate II, fig. 2) colored illustrations of several stages of the growth of a cell—its youth, its adolescence, its middle life, its advancing age, its extreme

old age.

Remember that a mass of bioplasm has a tendency to assume a more or less spheroidal form. But it changes itself in the course of a minute into all the protean shapes indicated here, first by the black, then by the unbroken line, then by the broken red line, and divides and subdivides its edges, until at last it throws off this portion of itself, which has the same powers with its parent. (See plate I, fig. 3.)