CHAPTER XXXIII 



THE ENDOCRINE GLANDS AND 

 THEIR FUNCTIONS 



The great complexity of the structure of organisms, particularly 

 of those animals in the higher ranks of the animal kingdom, makes 

 necessary a means of regulation and coordination of the functions 

 of the organ systems individually and a means of intercommunica- 

 tion between them. This work is cared for in part by the nervous 

 system; but another agency of regulation is present in all higher 

 organisms and many of the lower forms of life, which is of first 

 importance in this respect, one so complex and interwoven with 

 other organs in carrying out its functions that it is not thoroughly 

 understood at the present time. The group of organs doing this 

 work we designate as the endocrine glands. They manufacture and 

 furnish the body with chemical compounds called hormones, a term 

 which refers to compounds formed in the body and capable of 

 encouraging or exciting activity in another part of the body; they 

 are chemical messengers. The endocrine glands pour their hormones 

 directly into the blood stream without the assistance of ducts, and 

 the blood carries them to other parts of the body ; but they are never 

 carried to the outside of the body directly, as in the case of secre- 

 tions from the glands of external secretion, and for this reason the 

 endocrines are often referred to as organs of internal secretion, or 

 ductless glands. 



The functions of the hormones are numerous, and current research 

 and investigation in the new field of endocrinology are constantly 

 presenting new activities and interrelationships of these secretions. 

 The field of endocrinology is comparatively new, and a complete 

 understanding of the complexities involved is impossible until fur- 

 ther research is completed. The mysterious manner in which the 

 endocrine organs produce their secretions, the hormones, the man- 

 ner in which they choose the raw materials, combine them, and 

 give forth products which are vital to the welfare and happiness 

 and often to the very existence of an organism, is of most intense 

 interest and of the greatest importance. 



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