HORMONES 



logical constitution of each sex and of each individual is attained. 

 The pars distalis of the pituitary gland stimulates the thyroid of tad- 

 poles, and in turn the thyroid secretion promotes the metamorphosis 

 of the larval form. The pars intermedia of the pituitai'y, and sometimes 

 adrenalin, regulate the color of the skin of amphibians and fishes, by 

 dispersing or concentrating the pigment gianulcs in the chromato- 

 phore cells. 



(3) Endocrine Interrelation and Balance. — A close functional re- 

 lation exists between the endocrine glands. Following Gley, we can, 

 consider "correlation" as the relation of one organ with another; 

 when it is a mutual correlation, we may call it "interrelation." Thus, 

 while the secretion of pancreatic juice caused by secretin is an example 

 of "correlation" between the duodenum and the pancreas, there exists 

 an interrelation between the hypophysis and the gonads, for if the 

 anterohypophysis is responsible for the final development and main- 

 tenance of the functional activity of the gonads, at the same time the 

 endocrine secretion of the latter regulates and moderates the gonad- 

 stimulating function of the hypophysis. 



Analysis of each separate endocrine gland or of each hormone is 

 clearly artificial. It was initially necessary because in order to study 

 the behaviour of a gland, there were no procedures available other 

 than extirpating the organ, injecting its extracts, and carrying out 

 anatomical and functional studies of clinical cases showing visible altera- 

 tions of some gland. Afterward the method persisted for didactic 

 reasons; but since no endocrine gland can be considered as if its action 

 were independent of other glands, the method is now being abandoned. 



A constellation of endocrine glands exists whose central organ 

 is the hypophysis, the function of each gland being influenced more or 

 less by the function of the others. Because the anterohypophysis con- 

 tributes to the development and maintenance of the structure and 

 function of various glands, extirpation of the pituitary produces a 

 marked atrophy and hypofunction of the thyroid, gonads, and adre- 

 nals, to such an extent that it has been said that the hypophysectomized 

 rat is an endocrinological and metabolic ruin. But, at the same time, 

 the structure and function of the anterohypophysis is governed by 

 hormones secreted by the thyroid, gonads, and adrenal cortex. 



Each gland produces very specific hormones which play im- 

 portant roles; nevertheless these hormones constitute simple parts of 



