CELLS. 61 



The nucleus grows less than the cell, because as soon as the latter is 

 formed it no lonjrer comes into direct contact with the concentrated 

 cytoblastema. General growth takes place when the molecules of the 

 membranes all attract equally; partial growth, when this happens only 

 or especially at particular spots, where the apposition of new matter 

 takes place to a greater extent. With reference to the mode of forma- 

 tion of precipitates and of crystals, this theory appears to me to ex- 

 plain very well the phenomena of general growth, supposing that we 

 ascribe to the cell-membrane the faculty of readily taking up molecules 

 and applying them to its increase. Such, however, must be the case, 

 for the relations of the nuclei, which even when free, never grow very 

 considerably, and particularly never in one direction,'^ show that the 

 power of growth is not simply innate in every organic membrane, mani- 

 festing itself when sufficient formative material is offered, but requires 

 peculiar conditions which are realized only in the cell-membrane. To 

 account for partial growth, Schwann's view must be somewhat extended ; 

 for only those modes of growth in which the cells, during their increase 

 in certain directions, lose nothing of their original dimensions in others, 

 can be interpreted in 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 mechani- 

 cal one. For the rest, it may be remarked, 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 in- 

 vestigated with care [see Remarks) ; but these have such peculiar rela- 

 tions 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 investi- 

 gation teaches us, it may be permissible to regard the cell-contents in 

 general, as a moderately concentrated 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 



* [Tins is surely incorrect. Tlie " nuclei" in the hair-pulp, in the tooth pulp, in connec- 

 tive tissue, in organic muscle, grow in one direction to a very considerable extent. — Tes]. 



