46 THE NEW PHYSIOLOGY. 



dioxide are steadied during the passage of the blood 

 through the systemic capillaries. The thread of organic 

 determination running through the working of those 

 processes, and the maintenance of the structures associ- 

 ated with them, is the biological thread, and the only 

 thing about them of any interest to a biologist as such. 



I have developed my argument against the mechanistic 

 theory from the point of view of the fully developed 

 organism. If we also take into account the phenomena 

 of development and reproduction, the argument becomes 

 still more conclusive. As if to convince us by an ocular 

 demonstration that the organic whole is in the parts, 

 Nature, in the reproduction of an organism, seems deli- 

 berately to scrap everything that might be supposed to 

 be mechanism, and then build the whole organism up 

 again out of one small part. A mechanistic theory of 

 heredity is to me, if possible, more unthinkable than a 

 mechanistic theory of the activities of a fully developed 

 organism. 



As scientific working hypotheses the mechanistic and 

 vitalistic theories of life are dead, though they will doubt- 

 less have to lie in state for many years before the scientific 

 world is convinced that they are dead. They took origin 

 side by side in observation which was not thorough, and 

 in thinking which was not clear. The distinctively 

 biological working hypothesis which is taking their place 

 is in reality nothing new ; for even though it has not 

 been clearly expressed, it has subconsciously guided 

 biological investigation and modes of thought and ex- 

 pression. The writings of such a man as Harvey are 

 instinct with it ; and it seems to me that it is in the light 

 of the guiding ideas and scientific example of Harvey 



