QUANTITATIVE SELECTIVE POWER 123 



given, only a portion of the product may diosmose from the cell, while 

 the rest is retained. 



That the formation of insoluble compounds is frequently the cause 

 inducing an accumulation of particular substances, is well illustrated by 

 the formation and growth of cell-walls, starch grains, crystals of calcium 

 oxalate, &c. The dissolved substances (sugars, salts of organic acids, potas- 

 sium nitrate. &c.) which are contained in the cell and which do not diosmose 

 from it, must be present in a non-diosmosing form, and must have passed 

 through the plasmatic membrane as diosmosing compounds. The fact 

 that the reactions for nitrates or reducing-sugar may be obtained on 

 testing dead cells, does not necessarily indicate that these substances are 

 actually present in this form in the living cell (Sect. 16), for the non- 

 diosmosing compounds may be stable only under the conditions presented 

 during its life \ 



With regard to non-essential substances, which are occasionally 

 absorbed and secreted in large amount, the same general principles hold 

 good. In the case of the aniline dyes, it has been definitely proved 

 that their passive secretion by the living cell is due to the formation of 

 non-diosmosing compounds as absorption continues. This must also be 

 the case with the soluble sodium compounds present in the plant, whereas 

 silica, which is often very abundant, is commonly deposited in an insoluble 

 form impregnating the cell-wall. 



All accumulation or excretion, dependent upon diosmotic exchange, 

 is governed by the above laws, independently of the precise manner in 

 which diosmosis is temporarily or permanently produced or rendered 

 possible. The passage through the cell-membranes is due to the action 

 of the same molecular forces which operate in the production of all 

 diosmotic exchange. This is still the case, when the accumulation of 

 a substance within a cell is due to the fact that the plasmatic membrane 

 allows particular molecules colliding against it to pass through only in 

 one direction, so that they enter the cell but cannot escape from it 

 (Sect. 1 6). 



An accumulation might also take place by vitalistic means, either 

 by the aid of plasmatic movements, or by some other manifestation of 

 energy directed to this end, the molecules of the given substance being 

 forcibly transferred through the protoplasmic substance and membranes 

 (Sect. 16). It is true that there is at present no evidence pointing to 

 the existence of any such power, or indicating that the plasmatic membrane 

 may be permeable to certain substances in one direction only. Never- 

 theless, it seems quite rational to suppose that among its varied powers, 

 the living organism is able in particular cases to employ special means 



1 Pfeffer, 1. c., p. 309. 



