136 



THE CELL 



Marine plants show most clearly, in what very unequal propor- 

 tions, they absorb from the multitude of salts offered them in sea- 

 water, the ones which are necessary to them. For instance, they 

 only store up very small quantities of common salt, of which about 

 3 per cent, is present in the water, whilst, on the contrary, they 

 take up relatively large amounts of potassium, magnesium, and 

 calcium salts, of which there are only traces. And in a similar 

 manner, the analysis of the ashes of different land-plants which 

 have flourished side by side in the same earth yields very different 

 results. 



Investigation of the metabolism occurring in the animal 

 body leads to the same conclusion. Only certain cells have 

 the tendency to take possession of the lime-salts, which are 

 present in almost inappreciable amounts in the fluids of the 

 body, and to deposit them in the osseous tissues ; other groups 

 of cells, such as those in the kidneys, take up the substances 

 from the blood, and excrete them in the form of urine ; others 

 store up fat, etc., etc. 



The factors concerned in this absorption and non-absorption of 

 matter are at present quite beyond our comprehension. It is 

 curious that the need which is evinced by the economy of a cell 

 for a certain substance does not always imply that this will be 

 taken up. Cells may absorb materials which are either directly 

 hurtful or completely useless to them. In this respect the very 

 different ways in which living plant cells take up aniline dyes are 

 very instructive (Pfeffer V. 22b). 



Although solutions of methylene blue, methyl violet, cyanin, 

 Bismark brown, fuchsine and safranin, are absorbed, those of 

 nigrosin, aniline blue, methyl blue, eosin, and congo-red, are not 



