12 THE ACTION OF THE LIVING CELL 



ing chapters, many experiments conducted in divers 

 ways have demonstrated that these results and many 

 other biological phenomena may be explained by the 

 hypothesis that when injured, cells liberate cytost into 

 their surrounding fluids, and depending upon the 

 amount of this substance liberated, other tissues in con- 

 tact with these fluids are affected in one manner or an- 

 other. Carefully controlled experiments have shown 

 that when the latter are brought into contact with the 

 cytost of the same species, the growth and activities of 

 tissues are stimulated if the amount of cytost in the 

 surrounding fluids is small. On the other hand, if the 

 concentration of cytost in such fluids is too great, the 

 activities of the cells are inhibited, often to such an 

 extent that death ensues. 



The theories of the writer are the logical out- 

 growth of certain observations which were made con- 

 cerning the nature and cause of shock. In order that 

 the reader may follow the development of the writer's 

 concepts and thereby be prepared for the discussion 

 of the very interesting experiments made in the 

 writer's laboratory in recent years, we shall consider 

 in more or less chronological sequence the various ex- 

 perimental investigations which have led to the devel- 

 opment of those concepts. 



At the outset it should be noted that although from 

 time to time the author has enjoyed the collaboration 

 of several competent chemists, all attempts to isolate 

 and characterize cytost as a definite chemical entity 

 have been disappointing. Its presence, like that of 

 the enzymes and hormones, is made manifest only by 

 its action upon the living cell. 



