52 PRINCIPLES OF FEEDING FARM ANIMALS 



of the protein molecule is not of the nature of an explosion 

 resulting in a large number of fragments scattered about, 

 but instead it may be looked upon as a kind of slow erosion 

 whereby certain projecting pieces are rubbed or broken oIT. 

 . . . absorption takes place rapidly and the erosion prod- 

 ucts have a tendency to disappear from the alimentary 

 canal." 



Any proteins which have escaped digestion and absorp- 

 tion thus far are then passed on into the large intestine, where 

 the action of the trypsin and erepsin may continue for some 

 time. Here the proteins are attacked also by bacteria, 

 and putrefaction takes place with the formation of the same 

 products as formed in tryptic digestion, proteoses, peptones, 

 peptids, and finally amino acids. The amino acids are at- 

 tacked by bacteria, with the formation of such products 

 as indol, skatol, amines, ptomaines, and hydrogen-sulphide, 

 which, if absorbed in large quantities, may act as toxins to 

 the animal organism. A part of the products of digestion 

 in the large intestine is absorbed through the capillaries of 

 the intestinal walls and passes via the portal vein through 

 the liver into the general circulation. Any undigested or 

 unabsorbed residues are excreted in the feces. 



Nitrogen-free Extract. — Nitrogen-free extract consists of 

 all the carbohydrates in the feedingstuff except those in- 

 cluded under crude fiber. The principal constituent of the 

 nitrogen-free extract of most feedingstuff s is starch. Of less 

 importance is sucrose or cane sugar. Lactose or milk sugar 

 is the principal constituent of the nitrogen-free extract of 

 milk. 



The first digestion of starch occurs in the mouth, where 

 the saUvary amylase, if present, acts upon some of the starch 



