CHAPTER V 

 HOW THE GLANDS INFLUENCE THE NORMAL BODY 



The origin of the remarkable differences between individuals 

 that distinguish species, varieties and families, has long been one 

 of the chief puzzles of biology. It may indeed be called the lead- 

 ing puzzle, which led Darwin on to the collection of the data that 

 culminated in the "Origin of Species." The why of the Unique 

 is the fundamental problem of those who would understand life. 



An explanation is an attempt at a consistent and persistent, 

 sometimes an obstinate clarity of mind. A vast number of ob- 

 servations gathered by laboratory experimentalists as well as by 

 those naturalists of the abnormal, physicians in active practice, 

 prove that the construction of the individual both during de- 

 velopment before maturity, and maintenance during maturity, 

 his constitution, in short, is directed by the endocrine glands. 

 It is possible now to present an explanation of the individuality 

 of the individual. 



To assert that variation is responsible for the individual, that 

 it is the mechanism which isolates him as a being like none other 

 of his fellows, not even his parents, brothers, and sisters, is 

 merely to beg the question. What is variation? The internal 

 secretion theory of the process offers, for the first time, an 

 explanation that is coherent and comprehensive, based upon con- 

 crete and detailed observations. It provides an adequate inter- 

 pretation of the numberless hereditary gradations and transi- 

 tions, blendings and mixtures. It suggests a control of heredity 

 in the future. 



The Pure Types 



In the pure types, only one gland, either by being present in 

 great excess above the average, or by being pretty well below 

 the average, comes to exercise the dominating influence upon the 

 traits of the organism. As the strongest link in the chain, or as 

 the weakest, it rules. The others must accommodate themselves 

 to it. Among them as commanders of growth, development and 



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