SPIRAZINES 



One of the most remarkable characteristics of 

 living organisms is that all normal physiological 

 functions can take place while growth is in prog- 

 ress. In this respect living organisms differ from 

 artificial contrivances, which usually cannot per- 

 form their intended functions while they are in 

 the process of construction. Kegardless of whether 

 we are considering a multicellular or a unicellular 

 organism, its physical behavior does not seem to 

 bear any direct relationship to the chemical activ- 

 ity of the growing protoplasmic materials of 

 which it is composed. This peculiar independence 

 of behavior and growth can be explained only on 

 the theory that the specific structural character- 

 istics of protoplasmic materials are not changed, 

 either physically or chemically, by the addition of 

 amino acid molecules thereto. 



If the protoplasmic structures of living cells 

 were built up of discrete molecules of utmost com- 

 plexity, as is generally supposed, then it would be 

 impossible to explain the process of growth which 

 in nature takes place continuously and spon- 

 taneously by the assimilation of one amino acid 

 molecule after another. The synthesis of complex 



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