INTERNAL SECRETION 243 



extra resistance to fatigue is conferred upon the skeletal 

 muscles when adrenalin is sent to them. Thus, in an 

 emergency that might call either for flight or conflict the 

 animal is prepared for a maximum output of energy. We 

 have here a scientific conception of the "strength of des- 

 peration." 



The influence of other organs than those mentioned upon 

 the welfare of the organism as a whole is constantly being 

 studied. A great deal of attention is being given to the 

 very small but distinctly compound structure, called the 

 hypophysis, which is lodged beneath the brain in a hollow 

 of one of the cranial bones. Its relation to the course of the 

 metabolism is far from simple, but it seems to be clear that 

 it is an indispensable contributor to the circulating medium. 

 A much larger and more conspicuous affair, anatomically 

 speaking, is the thymus of young animals, a mass of cells 

 lying back of the breast-bone. It is the "neck sweetbread" 

 of the market. Since it is prominent during growth the 

 inference is natural that it ministers in some way to the 

 process of development. It almost vanishes at maturity. 

 It is not yet possible to make very definite statements 

 about the thymus. Removal does not seriously hinder the 

 progress of the growing animal. 



Here and there in the body are firm kernels of tissue, 

 spoken of as lymphatic glands or, better, as lymph-nodes. 

 These may be regarded as producers of internal secretion, 

 though it is probable that this description does not cover 

 all their activities. They are found especially in the neck, 

 the armpits, the groins, and in the mesentery. Wherever 

 placed, each is set upon the route of the lymph as it comes 

 from some region toward the chest. Thus the lymph-nodes 

 of the neck must be passed by the lymph that has had its 

 origin in the head, while those of the mesentery intercept 

 that which has come from the intestine. Microscopic 

 study shows that the lymph has to take a tortuous course 

 among the cells of the nodes. Looked at from a mechan- 

 ical standpoint these bodies are obstructions in the path. 

 They are also suggestive of filters. Their own cells are 



