CHAPTER XVIII 



THE HORMONE-CARRYING AND DISEASE-RESISTING FUNC- 

 TIONS OF THE BLOOD. BLOOD-CLOTTING 



Hormones. The chemical control of bodily processes by 

 means of hormones has assumed great importance of recent years 

 and is at present the subject of active investigation. For a long 

 time it has been recognized that many processes are subject to 

 hormone influence, but the number of such processes is being 

 constantly added to as our knowledge advances. Although a 

 few of the hormones have been isolated and their chemistry 

 studied, by far the greater number are known only by their 

 physiological effects. Most of the hormones are special substances, 

 formed in organs whose sole function, so far as we can judge, is 

 their production. A few of them exercise their hormone function 

 only incidentally to their chief bodily destiny. 



The functions of many hormones are associated with the proper 

 carrying out of ordinary bodily processes, as, for example, the 

 digestive process. Such will be considered in connection with 

 the study of those processes. Only those which are riot so asso- 

 ciated will be taken up here. 



The Ductless Glands. There are in the Body several organs 

 of such considerable size and so constantly present in vertebrate 

 animals that a priori they would seem to be of functional impor- 

 tance. Until quite recently, however, the functions of nearly 

 all of them were quite problematical, although it has long been 

 known that pathological changes in some of them were associated 

 with grave conditions of general disease. Even yet their physi- 

 ology is very incompletely known. 



When we speak of a true gland we mean an organ that forms 

 some definite secretion which it pours out in a separate form, but 

 the organs we are about to consider have no secreting recesses 

 and no ducts:. nevertheless they undoubtedly. make, and pass into 

 the lymph and blood, substances of great importance to the 

 healthy working of the Body, which we call hormones. 



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