DISEASES OF THE DIGESTIVE ORGANS 27 



In ruminants (cattle, sheep, goats), the mechanism of the 

 stomach is especially complicated. Solid food and medicines pass 

 into the rumen and reticulum and often remain, especially in the 

 rumen, several days. Medicines should therefore not be admin- 

 istered to cattle in solid form if a prompt effect is desired. On the 

 other hand, fluids or fluid medicines pass in part directly through 

 the omasum and abomasum into the intestines, where they are 

 rapidly absorbed and act promptly; the greater part, it is true, 

 passes into the reticulum and thence into the rumen. Rumination 

 results from the muscular activity of the rumen and reticulum and 

 the pressure of the inferior abdominal muscles. The necessary 

 conditions for the occurrence of rumination are a medium-full 

 rumen and a certain amount of fluid in the rumen and reticulum. 

 When the rumen is over-full or empty, or when the contents are dry, 

 rumination ceases. The correction of these defects, especially sup- 

 plying water when the contents of the rumen are dry, is of great 

 therapeutic importance in disturbances of digestion. For the same 

 reason, evacuating medicines which also stimulate gland secretions 

 (arecoline, pilocarpine) are to be preferred to the mere muscle 

 stimulants (eserine, barium chloride) in the treatment of impaction 

 of the rumen. 



The innervation of the stomach consists of the vagus and the 

 sympathetic nerves and the automatic gastric centres — one each 

 for opening and for closing the pylorus and the cardia. The motor 

 centre (vagus) is situated in the corpora quadrigemina; the inhibi- 

 tory centre (sjnnpathetic) in the spinal cord. Contraction of the 

 stomach wall may be produced by stimulation of the vagus nerve, 

 or reflexly by stimulation of the gastric mucous membrane (stimu- 

 lant stomachics). The secretion of gastric juice is influenced by 

 the vagus. 



2. Chemistry of Gastric Digestion. — The principal con- 

 stituents of the gastric juice are hydrochloric acid, secreted by the 

 glands of the fundus, and pepsin, secreted by the glands of the 

 fundus and of the pylorus. Other ferments, rennet, a fat-splitting 

 ferment, and a lactic acid ferment, are also present in the stomach. 

 The function of the gastric juice is a double one. Of first impor- 



