HIDDEN PROCESSES 159 



tion developed new properties which we say 

 are shown only by matter which is alive. 

 But only living matter can carry out these 

 transitions. They cannot be accomplished 

 by either b or c only by a. 



It is conceivable that it is by purely physical 

 processes that matters are taken up by the 

 living cell, so as to reach the protoplasm. 

 The thin layer of structureless matter lining 

 the wall of a living cell, and indeed, so far, 

 constituting the wall, may act like a mem- 

 brane used in physical experiments on osmo- 

 tic action. It is well known that such a 

 membrane may allow certain substances to 

 pass, while it is impermeable to other sub- 

 stances. The matters that can pass through 

 are soluble in the matter forming the mem- 

 brane, while insoluble substances are rejected. 

 In the living matter, the protoplasm, we have 

 seen that chemical processes occur. But 

 physical chemists know that many chemical 

 processes are reversible, that is to say, in the 

 first stage, from certain bodies (a) other 

 bodies (b) are formed, and in a second stage, 

 and under different physical conditions, (b) 



