CHAPTER III 



THE GROWTH-PROMOTING HORMONE OF 

 THE PITUITARY BODY 



IT IS impossible to state how many hormones are secreted 

 by the pituitary body. By means of various crude or re- 

 fined physico-chemical manipulations, many extracts 

 differing in their physiological or pharmacological effects 

 have been secured. The number of such extracts, however, 

 cannot be taken to correspond to the number of hormones 

 actually elaborated by the pituitary body. Some investiga- 

 tors believe that they may in part be cleavage-products of one 

 or more larger molecules. In the pars glandularis, for exam- 

 ple, the properties of the active extracts so far made suggest 

 either that the true hormones are protein-like or that they are 

 closely associated with protein-like substances. For purposes 

 of presentation in this chapter and in those succeeding it, 

 effects which appear to be peculiar to a particular extract of 

 the pars glandularis will be described as if they were due to a 

 particular hormone. From the standpoint of the physiology 

 of the pars glandularis in the normal animal, however, this 

 may not be true. 



Often it is not realized how limited a generalization can be 

 made concerning an extract which appears to be specific in its 

 effects. Any generalization as to the action of an extract of 

 the pars glandularis must take into account differences in the 

 response arising from variations in age, sex, race, diet, season, 

 method and frequency of administration of the extract, ease 

 of absorption of the extract, total dose, etc. It must always 

 be realized that very significant inherent differences may ap- 

 pear in the response of other animals — even of animals be- 

 longing to the same class and order. A further important con- 



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