THE DIGESTION OF THE NUTRIENTS 47 



horse, considerable digestion of the crude fiber may occur from 

 bacterial actions similar to those already described as taking 

 place in the rumen of cattle and sheep. Also, there is consid- 

 erable bacterial action upon the undigested proteins, causing 

 their putrefaction, with the formation of proteoses, peptones, 

 amino acids, and numerous other products, as indol, skatol, 

 amines, ptomaines, and hydrogen sulphide, which give to the 

 feces their offensive odor, and which, in some cases, are 

 toxic or poisonous to the animal organism if absorbed in 

 large quantities. After remaining in the large intestine 

 for some time, the undigested and unabsorbed feed residues, 

 together with remains of the digestive juices, living and dead 

 bacteria, and dead cells from the walls of the digestive tract 

 are passed on into the lower part of the large intestine, or 

 rectum, and excreted from the body through the anus as 

 feces. 



Absorption. — Absorption is the process by which the 

 final products of the digestion of the feed are taken into the 

 blood and lymph for final distribution to the tissues of the 

 body. The greater part of the digested food material is 

 absorbed from the small intestine, while smaller amounts 

 are absorbed from the large intestine. The wall of the 

 small intestine is lined with numerous, conical, round, or 

 club-shaped projections known as villi, which extend out 

 into the contents of the small intestine. Figure 9 shows 

 a cross-section of the mucous membrane of the small intes- 

 tine much enlarged. The partially digested food entering 

 from the stomach is poured })ack and forth in the upper end 

 of the small intestine in order to expose it sufficiently to 

 the absorbing action of the vilh. It is said that the contents 

 of the small intestine of the horse are passed to and fro twenty 



