Ill] THE DIGESTIVE ORGANS ' 49 



Seeing that pepsin can convert i)roteins into peptones and 

 erepsin can further change jieptones into amino-acids it has been 

 suggested by Reynolds Green that trypsin is in reahty composed 

 of a pepsin-like ferment together with an erepsin-like ferment. 



Erepsin is also manufactured by the pancreas, and according 

 to Vernon all (or nearly all) the tissues of the body have certain 

 ereptic properties and may therefore be regarded as forming this 

 ferment to a greater or less extent. 



Absorption. It is seen that by the time that the different 

 classes of foods have reached the hinder part of the small intestme, 

 they have all been brought under the influence of digestive 

 agencies, and so have to a large extent been reduced to a con- 

 dition of solution in which they can be absorbed into the cir- 

 culatory system. Absorption from the stomach is non-existent 

 or extremely slight, though it is said to occur to a somewhat 

 greater extent in the pig than in most other animals. As will 

 be seen later the large intestines are the main absorbing area 

 of the alimentary canal in many aninials. Nevertheless, in all 

 animals, absorption is carried on to a very large extent in the 

 small intestine and the villi which are very numerous are evidently 

 constructed to that end. 



These villi contain lymph vessels (lymphatics and lacteals) 

 which eventually communicate with the blood circulation. Fat 

 in the form of small globules is carried by leucocytes directly into 

 the lacteals. Moreover, the fatty acids diesolved in the bile 

 together with the glycerine are absorbed by the living cells of the 

 villi and recombined to form fat. The villi also contain blood 

 vessels and a small portion of the fat is absorbed directly into 

 the circulation and carried to the liver or is retained as fat in 

 the gut wall. The sugars (dextrose, levulose and galactose) are 

 also absorbed by the villi. Absorption in the small intestine 

 does not affect the products of protein digestion to the same 

 extent as the fats and carbohydrates, nevertheless amino-acids 

 as well as some of the intermediate products of digestion (e.g. 

 peptones) of this class of food stiiffs are also absorbed by the villi. 

 It was formerly thought that proteoses and peptones were re- 

 combined to form proteins during their passage through the 

 epithelial walls of the intestine, since the blood even in the 

 portal area does not normally contain any trace of peptone or 

 proteose. Later evidence has shown that most, if not all, of the 



