THE GROWTH-PROMOTING HORMONE 



sideration is whether the effects are observed in normal or in 

 hypophysectomized animals. 



It is well known that the removal of the pituitary body 

 from young and growing animals may markedly inhibit 

 growth. A priori it would be expected that the administra- 

 tion of the pituitary or of extracts made from the pituitary 

 would cause a resumption of growth in animals abnormally 

 small because of a previous hypophysectomy. Furthermore, 

 because gigantism and acromegaly in man appear to be due to 

 a hyperfunction of the pars glandularis, it would be expected 

 that growth at a faster rate and beyond the normal could 

 be brought about by the administration of the pituitary. In 

 certain animals both of these expectations have been realized. 



The use of the term "growth," however, requires a brief 

 consideration. Depending upon the investigator, growth is 

 judged by different criteria which usually are narrow and re- 

 stricted rather than broad and comprehensive. An increase 

 in the weight of the body is frequently taken to be synony- 

 mous with "growth." This is an imperfect but nevertheless 

 important indication of growth. An increase in weight is the 

 most characteristic result of the administration of the 

 growth-promoting hormone; in experimental gigantism it of- 

 ten is a more prominent change than an increase in the di- 

 mensions of the body or of some of its parts. A truer growth- 

 promoting effect is obtained by the administration of the an- 

 terior pituitary to animals hypophysectomized when young; 

 in such animals both the body-weight and the body-size are 

 strikingly increased by the treatment. Other characteristics 

 of growth in relation to growth-promoting extracts of the pars 

 glandularis have been studied much less frequently. 



The pituitary is of no importance probably in early embry- 

 onic growth; but in later embryonic life it possibly affects the 

 rate of growth. After birth, the rate of growth, the ultimate 

 body-size, and the shape of the body and its parts are de- 

 pendent only in part upon the normal functioning of the pars 



