PART VIII 

 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



CHAPTER LXXXI 

 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



In order that the various activities of the animal organism may act 

 efficiently as a whole, it is necessary that those of one part be correlated 

 with those of another. This correlation of function is mediated either 

 through the nervous system or through the action on one part of the 

 body of substances produced in another part and carried between them by 

 the blood. Control through the nervous system is especially developed for 

 those functions which have to be brought promptly into play, such as 

 muscular movement and the other physiological processes concerned in the 

 adjustment of the organism to quickly changing conditions of its environ- 

 ment. Control through the blood is the mechanism by which the metabolic 

 activities of different organs are mainly correlated. The chemical sub- 

 stances involved are often called internal secretions. 



Some of these internal secretions are merely by-products of metabolism, 

 and are only incidentally used for the purpose of bringing about control 

 between different parts of the body. To this group belong carbon dioxide, 

 which may act on the respiratory and other nerve centers, and urea, which 

 may stimulate increased activity of the kidneys. Indeed, the list of sub- 

 stances included under such a definition of internal secretions is almost 

 illimitable, and to designate by the special name of hormone every con- 

 stituent that can affect physiological functions, as some have done, can lead 

 only to confusion. The internal secretions with which we are more 

 directly concerned are those that are specially produced for the purpose 

 of controlling the metabolic functions. They are given the general name 

 of autacoids (E. A. Schafer). 60 Autacoids may be either the sole product 

 of some special gland or a secondary product of glands which have other 

 functions. To the former class belong the autacoids produced by the para- 

 thyroid, thyroid, pituitary and adrenal glands, and to the latter, those 

 produced by the pancreas and generative glands. 



Autacoids have further been subdivided by Schafer into two classes 



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