ON ARTIFICIAL CELLS 117 



ice, which, as he points out, is also a " liquid 



jelly-" 



Whether, the " oily " films form tubes or bubbles, 

 and foam-cells joining on to one another, depends 

 on the viscosity of the oily liquid. 



By an " oily " liquid he means one which has 

 surface-tension in the common surface with other 

 liquids with which it may be in contact. Thus a 

 solution of any salt in comparison with pure water, 

 or a weaker solution, may be called an oily liquid, 

 "Foam-cells" are thus formed, and if these cells are 

 very small and their walls very thin, the whole is 

 called a liquid jelly. The mutual inclination of the 

 foam-walls, and their surface-tensions, change with 

 the concentration of the oily liquid. 



Now these foam-cells, in a liquid jelly immersed in 

 water, apparently grow or diminish in size by the 

 diffusion of water inwards and outwards. And 

 liquid jelly can, by the presence of these cells, 

 for the time being, become doubly refracting when 

 the cells of their walls are expanded or contracted, 

 thus behaving like crystalline bodies. 



The very beautiful work of Lehmann, moreover, 

 illustrates the optical effects produced in a somewhat 

 similar way. But it is a matter of some difficulty to 

 decide whether these doubly refracting bodies are 

 really crystalline or merely of the nature of the foam- 

 cells just described. In any case they are not, it 

 would appear, in any sense alive, and not even like 

 the active petroblasts of von Schron. 



Their appearance on the whole suggests that they 



