ELEMENTS OF STRUCTURE. 81 



points to the conclusion that, as in the growth of the cell, so also in its 

 transmutative functions, the body takes the most prominent part, for in 

 it the most important alterations are observed to take place. The nucleus 

 seems to stand between the inert membrane and active body of the cell 

 in point of energy in the metamorphosis of matter. 



Of the amount of transmutation in large groups of cells of particular 

 tissues we know just as little. There are physiological facts, however, 

 which would lead us to the conclusion that those tissues to which we 

 ascribe the highest physiological dignity as, for instance, those of the 

 muscular and nervous systems possess this power to a very considerable 

 extent ; so that we may look on the cells of unstriped muscle and of gan- 

 glia as structures possessing the capability of rapid renovation of their 

 substance. But the coming and going of material must be still more rapid 

 in those numerous cells which clothe the interior of the glands of our 

 body, from all we know of the processes of secretion. On the other hand, 

 we find certain kinds of cells whose transformative abilities are probably 

 very inconsiderable, as, for instance, those of old laminated epithelia and 

 of nail- tissue (so closely related to that of the epidermis), and the cells 

 of cartilage. In respect to many other cellular structures, we are not 

 even able to form likely conjectures. 



The consideration of the means employed by nature to bring about this 

 transmutation of matter in the animal cell, is likewise bound up with 

 many difficulties. 



Among these agencies, however, may be reckoned, in the first place, the 

 property of imbibition inherent in histogeuic materials; and, secondly, 

 great stress must be laid upon the processes of endosmosis always accom- 

 panying cell-life. And in that chemical processes are incessantly at work 

 in the interior of the cell, and aro often of considerable energy ; in that 

 constant series of transmutations follow one upon another here, and that 

 the contents of the element change their nature very frequently; in that 

 fluids of different constitution pass over the surface of the cell finally, the 

 phenomena of diffusion must be very various. 



Looking somewhat more closely into the vital actions of the cell-sub- 

 stance, we find them to be of two kinds : "egotistical," or occurring in the 

 interests of the proper nutrition of the latter ; and again of another 

 nature, for the attainment of greater ends no longer confined to the narrow 

 purposes of cell-life. The latter are to be observed in gland cells. 



The mode of action of these is two-fold, with transitions from one 

 to the other. Certain cells only receive into their bodies substances 

 which existed previously in the blood, and which pass through them 

 without undergoing change, into the ducts of the gland, to form the pecu- 

 liar secretion of the latter. Thus, in the case of the gland-cells of the 

 kidney, for instance, we find them simply allowing of the passage through 

 them of certain constituents of the blood, namely, urea, uric and hippuric 

 acids, and several salts. It is probable, also, that the cells with which 

 serous sacs are lined admit of the transudation, in a similar manner, of 

 the fluids with which they are moistened and lubricated. On the other 

 hand to return to the gland-cells we find a considerable number of 

 glandular organs which do not constitute simple apparatuses for the fil- 

 tration of constituents of the blood, but which receive, on the contrary, 

 certain matters into their interior in order to transform them to cause 

 them to enter into new combinations, or to split them up into new com- 

 pounds, and so on. The tendency to refer all this chemical change to the 



