GASTRIC DIGESTION. 379 



serves to keep back the aliments that are not thoroughly digested. In 

 other respects, gastric digestion in ruminants is similar to that seen in 

 other animals. In other words, albuminoids are converted into peptones • 

 gelatin is dissolved and converted into a diffusible gelatin peptone and 

 milk is coagulated and its casein is converted into peptones. Adipose 

 tissue is dissolved and the oil liberated and partially split up into fatty 

 acids ; cane-sugar is slightly converted into inverted sugar through the 

 action of the acid ; starch which has escaped being converted into suo-ar 

 through the action of saliva in the rumen passes into the intestine to 

 be acted on by the intestinal secretions, for the degree of acidity of the 

 gastric juice is sufficient to interfere with the diastatic action of pt3'alin. 

 Gastric digestion in ruminants is much more complicated than in other 

 animals, and comprises a series of operations which are carried on partly 

 simultaneously and partly alternately. The two first reservoirs are 

 concerned in rumination and in the maceration of food. The third 

 stomach has nothing to do with rumination, but acts as a strainer and 

 prevents substances passing into the fourth stomach until sufficiently 

 comminuted and softened to be subjected to the action of gastric juice, 

 while, finally, the fourth stomach is the true digestive organ, in which 

 the albuminous contents of the food are converted into peptone. It is 

 thus seen that gastric digestion in the ruminant is much more complete 

 than in other herbivora. Therefqre, gastric digestion in these animals is 

 predominant, while intestinal digestion is simplified. 



8. Gastric Digestion in Birds. — Gastric digestion in birds differs 

 very essentially from that of mammals, the difference being dependent 

 on the difference of plan on which the alimentary tract is constructed. 

 The digestive parts are simplest in birds of prey, such as the owl, the 

 buzzard, and hawk. The oesophagus is large and dilatable, and is, as a 

 rule, not supplied with a crop. It is continuous, without any marked 

 line of demarcation, with the small longitudinal stomach, which takes on 

 a transverse curve where it ends in the small intestine. Where the 

 oesophagus terminates it has a calibre almost as great as the stomach, 

 so that the latter seems simply to be a prolongation of the oesophagus. 

 The superior limit of the stomach is marked by a band of large glands, 

 which may often be seen from the outside of this organ, and which 

 almost seem to resemble the agminated glands of the small intestine of 

 the mammal. Below this the stomach contracts, and again dilates to a 

 more or less globular pouch, and again becomes contracted and united 

 with the small intestine. The pyloric orifice in birds of prey is very 

 narrow. 



In gallinaceous birds, such as the cock, the turkey, and the pheasant, 

 the gullet dilates at the lower portion of the neck (the crop) and then 

 contracts, to again expand and form the ventriculus, which has thick, 



