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THE AMERICAN NATURALIST [Vol. XLII 



accomplished only in small part by professed physiolo- 

 gists. Not even has the evolution of function— a field of 

 great possibilities— been explored, except in a few small 

 and isolated spots. The necessity of properly controlled 

 experimentation in settling the vexed problems of evolu- 

 tion is, however, at last being recognized, and the next 

 few decades promise to witness great advances in the 

 discovery of the ways in which nature has made her 

 great experiment. 



It is not strange that with its intricacies and peculiar 

 difficulties the solving of the problems of nervous func- 

 tion has proceeded slowly. The facts that nervous func- 

 tion is a property of the nerves, and that the brain is the 

 seat of the mind were probably first capable of scientific 

 proof by the Alexandrians in the fourth century before 

 Christ. The two great functions of sensation and motion 

 were also recognized by the ancients, but that they were 

 mediated by different nerves was first demonstrated by 

 Sir Charles Bell, so late as 1811. The idea of the specific 

 energy of nerves— a phrase which means specific ac- 

 tivity—or the general principle that each nerve has 

 specific functions with which it always responds, no 

 matter how stimulated, was definitely proposed by 

 Johannes Miiller in 1826 for the nerves of special sense, 

 and later was generalized for other nerves and other 

 tissues. Since then great progress has been made in 

 discovering by experiment the specific functions of indi- 

 vidual nerves and in formulating therefrom theories of 

 the general functions of nervous tissues. That different 

 nervous activities are associated with different portions 

 of the brain was early surmised, and before the middle 

 of the past century such important nervous centers as 

 those controlling respiration and the beat of the heart 

 became located. Since then the nervous mechanism of a 

 host of unconscious organic processes has been discovered. 

 That the psychic portion of the brain does not function 

 as a unit, but consists rather of a complex group of 

 nervous organs, each with its specific functions— a fact 



