INTRODUCTORY 7 



gastric juice is, and which, like these two, plays an 

 important role in the digestion of foodstuffs. 



The double property of producing both an in- 

 ternal and an external secretion, which character- 

 izes the small intestine, is found in a number of 

 other tissues. The external secretion of the pan- 

 creas, for example, is the pancreatic juice, which 

 is carried by means of a duct to the small intestine. 

 But it has been shown that the removal of the 

 pancreas, or, what is the same thing, the removal 

 with it of an internal secretion developed by the 

 organ, and which finds its way into the blood, 

 gives rise to the dreaded sugar disease commonly 

 known as "diabetes." It would seem, therefore, 

 that the utilization of sugar by the liver the organ 

 that stores sugar and gives it out when necessary 

 is controlled by an internal secretion developed 

 by the pancreas. 



The generative glands (ovary and testicle) show 

 an internal and external secretion. The external 

 secretion contributes to the reproduction of the 

 species; the internal secretion plays a part in the 

 development of male and female characteristics. 

 One has but to think of the eunuchs in oriental 

 countries, or of animals from which, for commer- 

 cial reasons, the generative glands are removed, to 

 realize what effects are produced by removal of 

 these glands. But this will be treated more ex- 

 tensively later. 



