ORGANIC REGULATION 97 



no mere "functional" change, but is also "structural," 

 as shown, for instance, by thickening of the epithelium. 



When structural elements are destroyed or actually 

 removed, the process of reproduction is limited in the 

 higher organisms. We then observe the phenomenon 

 of other parts with similar function taking on the 

 special functions of the lost part. Gradual recovery 

 owing to other parts performing missing functions is a 

 matter of everyday experience in Medicine and Sur- 

 gery ; and though the evidence is to a large extent still 

 indirect, we cannot doubt that in all such cases struc- 

 tural changes are associated with the functional adap- 

 tation. The phenomena of vicarious function are also 

 quite clearly adaptive changes, i.e., changes of such a 

 nature that the life of the organism maintains as a 

 whole its identity. 



When one regards the facts of memory from the 

 purely physiological standpoint it is evident that 

 memory is a phenomenon of the same nature as adap- 

 tation. An experience or effort which has been gone 

 through leaves its mark in the body as increased power 

 of reaction to a similar experience or performance of a 

 similar effort, just as an attack of an infectious disease, 

 or vaccination, leaves its mark in a power of quickly 

 repelling a similar infection. Were it not so memory 

 would be a useless incumbrance. 



In this connection we may recall the facts relating 

 to the effects of practice in the carrying out of any 

 operation, such as writing, riding a bicycle, or playing 

 a musical instrument. Here frequent repetition of 

 what was at first a difficult and very imperfectly per- 



