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HORMONES 



B. A. HOUSSAY, director of the institute of biology and 



EXPERIMENTAL MEDICINE, BUENOS AIRES 



Definition and Significance 



'HE HORMONES are specific chemical substances pro- 

 duced by an organ or tissue which, after being discharged 

 into the circulating fluids (milieu inter ieur), may reach all parts of the 

 organism and in small amounts markedly influence the functions of 

 other organs or systems without themselves contributing important 

 quantities of matter or energy. 



This definition diff"erentiates them from other important sub- 

 stances which also reach the circulating fluids, such as: (a) nutritive 

 substances which supply the tissues with materials and energy as, for 

 example, glucose, amino acids, lipids, etc.; (b) vitamins, organic chemi- 

 cal regulators contained in the food; (c) chemical mediators of nerve 

 action, liberated by the nerve endings in the close vicinity of effector 

 or other nerve cells and which exert a localized action; {d) the organizers, 

 embryonic substances of regional origin which govern the differentia- 

 tion of a determined organ, even if transplated to another zone or culti- 

 vated in vitro; (e) the parhormones (Gley) which, although being excre- 

 tory substances produced by the metabolic processes of all the tissues, 

 nevertheless perform important regulatory functions, as is the case for 

 carbon dioxide in the regulation of respiration. 



The action of what we today call glands of internal secretion 

 is due to the hormones they produce; and the insufficiency of these 

 glands, therefore, is only a matter of hormone deficiency. 



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