348 



COMPARATIVE PHYSIOLOGY. 



There are two points that are very far from being deter- 

 mined: the one the fate of the products of digestion; the other 

 the exact limit to which digestion is carried. How much — e. g., 

 of proteid matter — does actually undergo 

 conversion into peptone; how much is 

 converted into leucin and tyrosin; or, 

 again, what proportion of the albuminous 

 matters are dealt with as such by the in- 

 testine without conversion into peptone 

 at all, either as soluble proteid or in the 

 form of solid particles ? 



1. It is generally believed that solu- 

 ble sugars are absorbed, usually after 

 conversion into maltose or glucose, by 

 the capillaries of the stomach and intes- 

 tine. 



2. There is some positive evidence of 

 the presence of fats, soaps, and sugars in 

 unusual amount after a meal in the por- 

 tal vein, which implies removal from the 

 intestinal contents by the capillaries, 

 though, so far as experiment goes, the 

 fat is chiefly in the form of soaps. 



Certain experiments have been made 

 by ligating the pyloric end of the stom- 

 ach, by introducing a cannula into the 

 thoracic duct, so as to continually remove its contents, etc. 

 But we are surprised that serious conclusions should have been 

 drawn under such circumstances, seeing that the natural condi- 

 tions are so altered. What we wish to get at in physiology is 

 the normal function of parts, and not the possible results after 

 our interference. Under such circumstances the phenomena 

 may have a suggestive but certainly can not have a conclusive 

 value. 



It is a very striking fact that little peptone (none, according 

 to some observers) can be detected even in the portal blood. 

 True it is, the circulation is rapid and constant, and a small 

 quantity might escape detection, yet a considerable amount be 

 removed from the intestine in the space of a few hours by the 

 capillaries alone. Peptone is not found in the contents of the 

 thoracic duct. 



For a considerable period it has been customary to use the 



Fig. 285.— Intestinal villus 

 (after Leydig). a, a, a, 

 epithelial covering; 6, b, 

 capillary network; c, c, 

 longitudinal muscular 

 fibers; d, lacteal. 



