I 6 INTERNAL SECRETION 



Starling's idea, that many of the by-products of organic activity 

 have become hormones only because certain apparatuses have a 

 specific sensibility for them, seems very probable. 



Our knowledge of the chemistry of hormone formation is very 

 slight. All that can be affirmed with certainty is that substances 

 of f widely different origin and of the most varied chemical com- 

 position may operate as stimulating agents. Internal secretions 

 may result from complicated synthetic processes, as iodothyrin 

 in the suprarenals ; they may be of very complex chemical 

 structure, as adrenalin, which is a methylamino-alcohol of pyro- 

 catechin ; but they may just as easily be the simple products of 

 decomposition, as carbonic acid and lactic acid. 



As far as we know at present, the sole characteristic which 

 all hormones possess in common is a negative one. They cer- 

 tainly do not belong to that group of substances which are known 

 as antigens, which, according to Ehrlich, possess a haptophoric 

 affinity with protoplasm and one or more by-affinities which are 

 determined by specific activities. The hormones resemble the 

 antigens in that, like the latter, they are active in minimal 

 quantities, but they differ in certain essential points. The 

 hormones do not require a period of incubation and, what is still 

 more important, they never provoke the formation of antibodies. 

 These negative properties of hormones are readily understood 

 when considered in the light of their physiological activity. The 

 accomplishment of rapid adjustments and the frequent repetition 

 of the same form of activity, are not functions which can be 

 performed by agents which are antigenic in character. 



It is for the future to supply a minute characterization of 

 the individual hormones and to decide whether their activity 

 arises from their chemical constitution or is due to other chemico- 

 physical causes. 



SOURCES OF INFORMATION AND METHODS 

 OF INVESTIGATION. 



The oldest information about the internal secretions, and 

 undoubtedly the most valuable, is that derived from what may 

 be called clinical observation. 



The castration of males, whether of man or of the lower 

 animals, is a proceeding which illustrates in the clearest manner 

 the results of the suppression of an organic function. It could 

 not fail to be remarked that castration is followed, not only by 

 the cessation of sexual activity, but also by other phenomena 

 pointing to a deep-seated change in the nature of the entire 

 organism. These changes have long been very well known, and 

 are brought about for definite ends. For instance, the knowledge 

 that castration is followed by an increased deposit of fat is used 



