360 VETERINARY PHYSIOLOGY 



C. Gastric Digestion in Ruminants 



This is complicated by the act of rumination or chewing the 

 cud. The food is rapidly cropped and swallowed, being passed 

 into the reticulum and rumen. The more fluid part tends to 

 accumulate in the former cavity. At a convenient opportunity, 

 by contraction of these cavities and of the abdominal walls 

 and diaphragm, a bolus of their contents is regurgitated into 

 the oesophagus, which, by an antiperistalsis, passes it up into 

 the mouth, where it is thoroughly masticated and mixed with 

 saliva. It is then swallowed, and, by a contraction of the walls 

 of the pillars of the cesophageal groove, the third stomach is 

 drawn close up to the oesophagus and receives the bolus. After 

 straining through the leaves of the omasum this enters the 

 abomasum or true stomach, and is there subjected to ordinary 

 proteolytic digestion. This has been studied by making a 

 Pavlov's pouch in the abomasum of the goat. When no food 

 is taken the secretion is alkaline and has no peptic action, but 

 when food is taken hydrochloric acid is secreted and peptic 

 digestion occurs. An amylolytic enzyme converting starch to 

 sugar seems also to be formed, and its presence is confirmed 

 by the demonstration of its occurrence in the stomach of the pig. 



As the food lies in the rumen and reticulum, it is subjected 

 to the action of bacteria, by which the cellulose is partly 

 decomposed, and the cell contents thus set free for the action 

 of digestive enzymes. 



IV. INTESTINAL DIGESTION 

 A. In the Dog and Pig 



After being subjected to gastric digestion the food is gene- 

 rally reduced to a semi-fluid grey pultaceous condition of 

 strongly acid reaction known as chyme, and in this condition 

 it enters the duodenum. 



Here it meets three different secretions : 



Pancreatic secretion. 

 Intestinal secretion. 

 Bile. 



