216 THE DUCTLESS GLANDS 



1. Theories as to the Function of the Medulla 



Prior to the discovery of the active principle of the medulla 

 of the adrenal body, some authors considered that the gland had 

 an excretory function. Thus, MacMunn found hsemochro- 

 mogen in the gland, and especially in the medulla, and drew 

 the conclusion that in the adrenals a downward metamorphosis 

 of worn-out pigments haemoglobins and histohsematins is 

 taking place, and that the function of these organs is to pick 

 out of the circulation these worn-out or effete colouring matters 

 with their accompanying proteins. Others considered that the 

 waste products of muscular metabolism are eliminated by the 

 glands. Still others attributed a blood-destroying function 

 to the gland. But since the discovery of the pressor principle 

 the excretory theory has almost entirely been replaced by that 

 of secretion internal secretion. 



It is now generally admitted that most, if not all, of the 

 recognized effects produced by the administration of adrenal 

 extracts are to be ascribed to the adrenin which is contained 

 in them. Three questions immediately arise : Is adrenin to be 

 looked upon as the product of the secretory activity of the 

 medulla of the glands ? Is it actually poured out into the 

 blood-stream ? Supposing these questions to be answered in 

 the affirmative, then what is the use of this internal secretion 

 this hormone in the animal economy ? 



Kohn, from morphological considerations, is opposed to the 

 view that the chromaphil tissues have an internal secretion. 

 He is certainly justified in insisting that we have no right, 

 simply because adrenin has certain pharmacodynamical effects, 

 therefore to assume, without further definite evidence, that it 

 is one of the functions of chromaphil tissues to pour out this 

 substance into the blood-stream in order that it may produce 

 such effects upon certain tissues of the body. He considers 

 that the cells forming the medulla of the adrenal body and the 

 chromaphil tissues elsewhere are not " epithelial," and there- 

 fore cannot secrete. 



But the active substance of the adrenal medulla is of a very 

 exceptional and extraordinary character, and is not to be 

 classed with the less active bodies found in extracts of organs 

 and tissues generally, and the medulla of the adrenal body is 

 not a mass of chromaphil cells of irregular shape and indefinite 



