236 PHYSIOLOGY OF ALIMENTATION. 



proven true for all mammals examined. In adult life, 

 however, the lactase of the pancreas disappears very largely, 

 at times entirely, and the lactase of the intestinal mucosa and 

 its secretion decreases much in amount (and in some animals 

 disappears entirely) unless milk-sugar continues to serve as 

 an article of food for the adult animal. 



We have yet to discuss the mechanism of this adaptation. 

 A direct effect of the milk-sugar upon the pancreas from the 

 lumen of the intestine is practically impossible, for the pan- 

 creas is connected with the gut by only a slender excretory 

 duct, through which, moreover, during the periods of diges- 

 tion an uninterrupted stream of juice pours. It might be 

 thought that when an excessive amount of milk-sugar is fed, 

 some passes over into the circulation, for we can discover 

 milk-sugar in the urine; and this absorbed sugar might be 

 thought to act directly upon the pancreas. That this idea 

 is not correct follows from the fact that the intravenous 

 or subcutaneous injection of milk-sugar is not followed by 

 the appearance in the pancreas of an increased amount of 

 lactase. Neither does a subcutaneous or intravenous injec- 

 tion of one of the products of milk-sugar digestion, such as 

 galactose, accomplish this result. In order that this may 

 occur the milk-sugar must come in contact with the mucosa of 

 the intestine. 



We are indebted to VERNON l for a further analysis of the 

 problem. This author, who entirely confirms the experimental 

 findings of WEINLAND, has shown that through contact of the 

 milk-sugar with the intestinal mucosa a substance is produced 

 which is absorbed into the blood and which when it is carried 

 to the pancreas brings about in this organ an increased pro- 

 duction of lactase. This phenomenon belongs, therefore, in 

 the same group with those which we discussed under the 

 heading of the secretins. 2 We have here another example of 

 the chemical connection which exists between different organs. 



1 VERNON: Journal of Physiology, 1905. 2 See pp. 211 and 227. 



