226 



NUTRITION 



It is generally supposed that the internal secretion of the "islands of 

 Langerhans" of the pancreas has control over the oxidation or other 

 destructive metabolism of the dextrose of the blood and tissues. Schiiltze 

 finds evidence in addition that this product, like that of the pituitary 

 body, regulates the blood-pressure of the vessels. The internal secre- 

 tions of the duodenum have been already discussed in the chapter on 

 Digestion. Among these are secretin and kinase (entero-kinase). 

 Some claim that secretin is the product of all the tissues in the body as 



FIG. 120 



Tubular glands. 



Alveolar glands. 



A diagram of various typical forms of glands: a, duct; x, simple tubule; xx, simple 

 alveolus. (Szymonowicz and MacCallum.) 



well as of the duodenal wall. The internal secretions of the liver are 

 glycogen and an enzyme, sometimes called urease, which has the power 

 of forming urea from some of the decomposition-products of proteid. 

 Schafer suggests that perhaps by means of an internal secretion the liver 

 saves the iron from the breaking down red blood-corpuscles which 

 otherwise would be lost to the body. The thyroid, either by means of a 

 peculiar substance called colloid which collects in the alveoli (and 

 is absorbed by the lymph), or by less obvious products which pass 



