CELLS AND TISSUES. 33 



with ether-soluble substances in the protoplasm these 

 are such as cholesterin and lecithin, or, as OVERTON 

 calls them all, lipoids these gels are able to take up 

 substances which are not soluble in water. The man- 

 ner in which the lipoids are held by the cell plasma, 

 the nature of which is still unknown, must no doubt be 

 governed, according to our newer physico-chemical 

 conceptions, by some property of the lipoids, such as 

 their solution affinity. According to the extensive investi- 

 gations of OVERTON, the ability of many substances 

 soluble only with difficulty in water to enter the living 

 cell is dependent upon their solubility in the lipoids. 



If by the distribution coefficient of a substance between 

 two solvents we understand the relation between the 

 spacial concentrations which exist in these two solvents 

 after equilibrium has been established, it is found that 

 the distribution coefficient of many narcotics between oil 

 and water determines also their distribution between 

 medium (such as blood plasma) and cell contents (such 

 as the lipoids of the brain), and therefore also their effect 

 (MEYER, OVERTON). The investigations of FRIEDEN- 

 THAL on absorption by the intestine of substances insol- 

 uble in water also belong under this heading, which is of 

 such fundamental importance in many questions in physi- 

 ology. SPIRO has given numerous examples of the gen- 

 eral significance of the distribution law. No doubt experi- 

 ments carried out on simple models would bring much 

 light into this field. 



After what has been said, the similarity in important 

 physico-chemical properties between living matter and 

 certain gels must be looked upon as an extensive one. 

 Without doubt a continued investigation of the colloids 



