THE DUCTLESS GLANDS 4" 



they do not consist of epithelial, "secreting" cells, and belong 

 to quite a different category of organs, viz. the "haemolymph" 

 series (1). The structures usually included at the present time 

 under the title of " ductless glands " are the thyroid gland 

 (including the parathyroids), the suprarenal capsule consisting 

 of "cortex" and "medulla," the pituitary body consisting of 

 the "infundibular" or "nervous" portion and the "glandular" 

 portion, the thymus gland, and the corpus luteum. It is 

 believed that these " ductless glands " manufacture and pour, 

 directly or indirectly, into the blood stream some substance or 

 substances which are of service in the economy, either by 

 supplying a need, or by destroying other substances which are 

 needless or positively harmful. This last function, that of 

 " Entgiftung," is usually ascribed to the thyroid, though in 

 this, as in other cases, the two conceptions are not necessarily 

 antagonistic. 



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

 term " internal secretion " has probably 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 recognise an "enzyme" 

 in the fluid secreted, and are familiar with its action on food 

 as a process of digestion. Very different is the case, for ex- 

 ample, of the medulla of the suprarenal capsule. Here nothing 

 is known of any changes in the cells indicative of the act of 

 secretion, and the very fact that any secretion is poured into 

 the blood stream can only be shown by laborious and indirect 

 methods. It must be confessed, in fact, that many of our 

 conceptions of internal secretion rank little higher than plausible 

 hypotheses. 



But a typical gland having a duct and performing " external 

 secretion " may possess according to modern views in addition 

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

 the pancreas, the kidney, the testis, and the ovary (2). But in 

 the present article we shall confine our attention to the internal 



