CONSTITUTION OF LIVING MATTER 87 



with it, which is comparable with the differentiation 

 of cells. A foreign colloid may be thrust into it, but 

 it shows no tendency to diffuse, just as in intra- 

 cellular structures. Delicately shaded changes in 

 state are to be observed in these colloids, just as in 

 living matter, through the action of substances 

 within them. Thus, they become more solid or more 

 fluid, without change in their bulk, by the action of 

 crystalloids or enzymes ; the latter producing partial 

 or complete peptonisation. They also manifest the 

 phenomena of adsorption and a great degree of 

 selection with regard to the substances absorbed. 

 Living colloids are such as can take up substances 

 soluble in water or in ether. The latter are called 

 lipoids, e.g. cholesterin and lecithin. It is not known 

 how these lipoids are held by the protoplasm ; but 

 it is probably governed by some property of their 

 own, such as solution affinity. According to Over- 

 ton the ability of many substances insoluble in water 

 to enter the cells is entirely due to their solubility in 

 the lipoids of the protoplasm ; other substances also 

 enter the cells more readily, because of their solu- 

 bility in the lipoids, than their near relations which 

 are soluble in water. The effects of narcotics, for 

 instance, depend upon the distribution coefficient, 

 that is upon the rapidity and ease of their distribu- 

 tion between two media, such as the blood-plasma 

 and the cell-contents. The absorption of substances 

 insoluble in water from the intestine belongs to the 

 same heading. The similarity between the physico- 

 chemical properties of non-living gels and those 

 in living matter is therefore extensive, and this 

 renders them suitable for an investigation into the 



