B. A. HOUSSAY 



In a wider sense, which is not usual, internal secretion would mean 

 any specific cellular elaboration discharged into the internal medium. It is 

 in this sense that Claude Bernard considered glucose, which is produced in 

 the liver and then passes into the blood, as an internal secretion. 



As we all know, the glands of internal secretion are referred to 

 as such because they pour their elaborated products into the blood, 

 in contrast to the glands of external secretion which pour their products 

 out of the body or in cavities which communicate with the external 

 medium. 



The first demonstration of a hormonal action was the induction 

 of the comb of a capon by testicular graft (Berthold, 1849). The ex- 

 pression "internal secretion" was used for the first time by Claude 

 Bernard (1855) to point out that the liver "shed" sugar in the blood. 

 The concept of internal secretions as we now understand it is due to 

 Brown Sequard who, in 1891, stated in a paper with Arsonval, "Nous 

 admettons que chaque tissue, et plus g^n^ralement, chaque cellule 

 de I'organisme secrete pour son propre compte des produits ou des 

 ferments sp^ciaux qui sont versus dans le sang et qui viennent influencer 

 par I'interm^diaire de ce liquide toutes les autres cellules rendues ainsi 

 solidaires les unes des autres par un m^chanisme autre que le tissue 

 nerveux." The name "hormones" was proposed by Hardy to desig- 

 nate the "chemical messengers" (Bayliss and Starling, 1904) which are 

 secreted in the blood by one organ to stimulate the functions of another. 



Hormone etymologically means "I arouse the activity" or "I 

 excite," but we are now aware of the existence of inhibitory hormonal 

 actions. It is useless to classify the hormones as stimulating or inhibi- 

 tory, inasmuch as the same hormone may often produce both effects, 

 depending upon its concentration or the organ which it affects. It is 

 understandable, therefore, why the designations proposed by Sharpey- 

 Schafer, who gave them the general name of "autacoids" and sub- 

 divided them into "hormones" (exciting) and "chalones" (inhibitory), 

 did not gain currency. 



Chemical Nature 



According to their chemical nature the known hormones can be 

 classified into three groups: 



(7) Phenolic Derivatives. — Both adrenalin, the hormone of the 



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