DEFINITION OF "INTERNAL SECRETION" 15 



that of " Entgiftung," an "antitoxic" function is fre- 

 quently ascribed to the thyroid, though in this, as in other 

 cases, the two conceptions are not necessarily antagonistic. 

 We can readily imagine that a gland may manufacture a 

 definite internal secretion whose active principle may be 

 competent to destroy poisonous products in the blood-stream 

 or in some part of the body. 



It is, perhaps, desirable to point out at this stage that the 

 term "internal secretion" has been used too generally and 

 too confidently in many cases. Our knowledge of internal 

 secretion is not to be compared in accuracy and definiteness 

 with our knowledge of "external" or ordinary glandular 

 secretion. Thus, in the case of the submaxillary glands, we 

 can observe the various conditions, loaded or unloaded, of 

 the gland cells. We can watch the flow of the secretion, 

 and regulate it by stimulation of nerves. We can note changes 

 in the volume and blood-supply of the gland concomitantly 

 with the act of secretion. Finally, we can recognize an 

 " enzyme " in the fluid secreted, and are familiar with its 

 chemical action on the food as a process of digestion. Very 

 different is the case, for example, of the medulla of the adrenal 

 body and of the chromaphil tissues generally. Here com- 

 paratively little is known of changes in the cells indicative of 

 the act of secretion, 1 and the very fact that any secretion is 

 poured into the blood-stream can only be shown, if shown at 

 all, by laborious and indirect methods. It must be confessed, 

 as a matter of fact, that some of our conceptions in regard to 

 internal secretion are worthy to rank little higher than plausible 

 hypotheses. 



But a typical gland having a duct and performing " external 

 secretion" may possess also, according to modern views, the 

 function of "internal secretion." This applies to the liver, the 

 pancreas, the kidney, as well as the intestinal and gastric glands. 

 The liver has, besides the formation of the bile and the gly- 

 cogenic function (which, owing to its highly special character, 

 is usually not treated along with the internal secretions), 

 the still further duty to render innocuous the end-products of 

 protein metabolism. One of these end-products is ammonia ; 

 this is converted in the liver into urea. So that the distinctly 

 poisonous ammonia is transformed in the liver into the com- 



1 See, however, pp. 235, 237. 



