CHAPTER V 



THE DIFFUSION OF SUBSTANCES INTO LIVING CELLS 

 THE "COEFFICIENT OF DIFFUSION" 



THE following points regarding the diffusion of sub- 

 stances into cells have been determined by experimen- 

 tation with this method. A cell does not respond to the 

 action of a chemical substance unless the substance has 

 diffused into it. It is of the utmost importance, there- 

 fore, that the law T s w T hich are concerned in this diffusion 

 should be understood, both for the practical application 

 of this in-vitro method in the study of the actions of 

 substances on individual cells and also, I think, because 

 it throws light upon the way in which drugs produce 

 their effects upon the various systems and organs of the 

 animal body. Very little has hitherto been known 

 concerning the diffusion of substances into individual 

 living cells; and although we do not claim to have 

 advanced the knowledge of the subject to a very great 

 extent as far as its scientific basis is concerned, w r e can 

 safely say that w r e are now T in a position to cause sub- 

 stances to diffuse into individual cells according to our 

 will. We do not know 7 all the scientific facts, it is true, 

 for more \vork will be necessary before these can be 



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