71 



This is to a large extent a matter of terminology, but I fancy it 

 will be found in the long run most convenient to retain the terms 

 cortical and medullary in view of the intimate connections between the 

 two structures in Mammals. 



Kohn's views on the nature of internal secretion require a word 

 or two of comment. He points out that many tissues and organs 

 furnish an extract which produces physiological effects when injected 

 into an animal, and he justly remarks that we should not in all cases 

 assume that it is the function of the organ or tissue to manufacture 

 the active ingredient of this extract. Thus it has recently been shewn 

 (Osborne and Vincent, 19) that extracts of all parts of the nervous 

 system contain a substance which, when injected into the blood-vessels 

 of an animal, lower the blood-pressure. But it would be rash to 

 allege that to make this substance is one of the "functions" of the 

 nervous system ^), 



On the other hand from some organs such very exceptional sub- 

 stances can be extracted, and such very unusual physiological efiects 

 can be produced by their administration, that we are justified in 

 interpreting these effects as an indication of the function of the organ, 

 and looking upon the substances as the products of its "internal 

 secretion". Such an organ is the medulla of the suprarenal capsule. 

 The active principle of this "administered in the proportion of not 

 more than one-millionth part of a grm. per kilo, of body weight . . ., 

 is still sufficient to produce distinct physiological results upon the heart 

 and arteries" (Schäfer, 21). 



Surely this substance is something very exceptional and not to 

 be classed with the less active bodies in extracts of organs and tissues 

 generally. Besides, I would point out that it has not been shewn 

 that extracts of tissues (other than nervous and glandular) such as 

 muscles will produce any appreciable physiological effects. I have at 

 any rate failed to find any such effects (see 29 and other papers). 

 The fact is, that there is something very extraordinary about the 

 substance or substances present in the suprarenal medulla, and we 

 are, most physiologists will agree, warranted in attributing its presence 

 to a specific activity of the tissue-cells; and any tissue which can 

 manifest any such specific activity and which discharges the products 

 into the blood-stream must be called an "internally- secreting gland". 



It must be noted that it has not yet been proved that the carotid 



1) Extracts of thyroid and several other glands lower blood-pressure 

 (Schäfer, 21, p. 943). 



