CHAPTER XVIII 



THE HORMONE-CARRYING AND DISEASE-RESISTING 

 FUNCTIONS 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. 



As stated previously the organs whose exclusive function is to 

 secrete hormones are known as ductless glands. In spite of a great 

 amount of investigation in recent years our knowledge of the 

 chemical co-ordination of the Body is still very incomplete and 

 there are some ductless glands concerning whose function we have 

 virtually no information. Among these may be mentioned the 

 parathyroids, small bodies, usually four in number, which are found 

 on or near the thyroids, sometimes embedded within them. That 

 these produce an essential hormone is proven by the fact that their 

 complete removal is followed by acute toxic symptoms, with mus- 

 cular convulsions, ending in death. Of the normal functioning of 

 the hormone which they produce nothing significant is known. 



There are some hormones, which, instead of being elaborated in 

 specific ductless glands, are made by cells embedded in organs 

 whose primary functions have no relation with those of the hor- 

 mones made within their mass. The special hormone-producing 

 cells in these cases, although anatomically parts of the organs within 

 which they lie, are physiologically as distinct as though they 



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