CELLS. 37 



Schwann's way, but not those in which the cells become 

 narrower as they elongate; here we must assume that whilst 

 new substance is deposited in the one direction, in the other 

 an absorption takes place, for we can in nowise consider the 

 process to be a mechanical one. For the rest, it may be re- 

 marked, that partial growth may depend upon the occurrence 

 of assimilation, in particular cells, only in certain directions, as 

 in the thickened vegetable cells with pore-canals, which is 

 possibly connected with a one-sided direction of the currents 

 in the cell-contents. 



§ 15- 



Processes in the interior of the Cells. — In order to obtain a 

 clear conception of the processes which go on in the interior 

 of cells, it would before all things be necessary to have a more 

 exact acquaintance with the chemical composition of the cell- 

 contents than we at present possess. Only two kinds of cells, 

 the ovum and the blood-globule, have been investigated with 

 care (see Remarks) ; but these have such peculiar relations that 

 they can hardly be regarded as types of cells in. general. 

 However, we may from these analyses draw certain inferences 

 with regard to other cells, and bearing in mind what micro- 

 chemical investigation teaches us, it may be permissible to 

 regard the cell contents in general, as a moderately concen- 

 trated solution of protein with alkaline and earthy salts, and 

 dissolved or suspended fatty particles. From these common 

 characters, presented without doubt by all cells, at least in their 

 young condition, many cells differ very widely,insomuch as either 

 some of these constituents greatly predominate or altogether 

 new substances occur. Thus, there exist cells with much 

 protein, as the nerve-cells; and with much fat, as the fat-cells, 

 the cells of the sebaceous follicles, of the milk-glands, &c. ; — 

 then such as contain hsematin, pigment, biliary and urinary 

 constituents, mucus (epithelium cells), milk, sugar, &c. &c. 



The phenomena manifested by these, so variously constituted 

 cell-contents, during life, may be best enumerated as — absorp- 

 tion, assimilation, and excretion. These depend principally 

 upon chemical and physical conditions, and are to a great 

 extent capable of microscopic investigation, since very fre- 

 quently the changes of form in the cell and the changes of its 



