CELL FORMATION. 229 



transparent fluid, within which floats another smaller bag, 

 and in that another still smaller, which is perhaps more com- 

 pact, though it may also be hollow. This transparent fluid 

 may become slightly granular, or cloudy in appearance. Ap- 

 ply to it a high magnifying power, however, say of two thou- 

 sand diameters, and then we shall find that this cloudy fluid 

 resolves itself into grains, each of which is a hollow bag 

 resembling the larger cells. In fact, the egg itself, at first a 

 mere granule of yolk, hardly yet observed in its internal 

 structure, is in a later phase such a cell as I have described. 



It is now generally understood that all animal substances 

 are but the result of the multiplication and increase of such 

 cells, which assume different forms, dififerent consistency and 

 various combinations, being peculiarly modified and adapted 

 to every organ. Bone is nothing but an accumulation of cells 

 of very irregular form, in which limestone particles are con- 

 solidating. Flesh is nothing but elongated thread-like cells, 

 confined together in bundles. Cartilage is nothing but a com- 

 bination of cells, having thicker walls, of a more transparent 

 character. Every substance, in short, of which the body in 

 its adult condition is composed, be it brain, tendon, flesh, 

 blood, bone, skin, or the fluid secreted by the various glands 

 (unless they are merely material to be thrown oft" from the 

 body), are but various cells in their numerous modifications, 

 having their marked peculiarities in each substance, but when 

 first forming, exactly the same in all. Up to this time the cells 

 are alike, and are scattered uniformly throughout the whole 

 mass of the yolk, but by an impulse within the yolk itself, 

 neither modified by nor allied with anything else, — by an in- 

 ternal impulse, in short, — these cells at a given time begin to 

 multiply more rapidly on one side of the yolk than on the other, 

 and as they multiply, they become also smaller ; that is, the 

 new cells produced are smaller than the older cells from which 

 they are derived. These new cells accumulate upon one 

 side of the yolk and form a little whitish speck on its sur- 

 face. This is the beginning of a new being. It is so 

 merged in the rest of the yolk as hardly to be distinguishable 

 from it. You cannot mark the boundary between that field 

 of individualized cells and the adjoining yolk. Examined 

 from above, it is seen to be a hollow sphere, somewhat more 



