THE ANIMAL BODY— DIGESTION— METABOLISM 



23 



and so the action of the ptyalin on starch continues in this part of that 

 organ. The intestinal or rear end of the stomach, on the other hand, 

 secretes much acid. Here the action of the ptyalin ceases and pepsin 

 digestion becomes active. 



Pepsin, which acts only in weak acid solutions, converts the very 

 complex proteins into soluble and simpler, tho still complex, products 



Fig. 8. — Longitudinal Section of Stomach of the Horse 



A, Q'^sopliagiis, or gullet; b, oesophageal region of stomach, in which no gastric 

 juice is secreted; c, entrance of gullet; d, left extremity of stomach; e, boundary 

 between oesophageal region and portion of stomach secreting gastric juice; f. g, 

 fundus gland region and pyloric gland region, in which gastric juice is secreted; 

 h, pylorus, or ring of muscles closi'ng the stomach; i, entrance of pancreatic and 

 bile ducts. (From Sisson, "Anatomy of the Domestic Animals.") 



known as proteoses and peptones. Bennin, the other enzyme of the 

 gastric juice, changes milk into a solid curd. Were it not for this, 

 milk would pass on quickly into the small intestine before its proteins 

 had been digested by pepsin. 



Soon after the food reaches the stomach, its walls begin a series of 



