GASTRIC DIGESTION. 



375 



ougbly macerated and soaked in fluid, and from which they are forced 

 into the resophagus during rumination or into the honey-comb bag dur- 

 ing the intervals of rumination. It is evident, therefore, that the food 

 contained in this pouch may undergo changes due to the movements to 

 which it is subjected, the temperature, and the action of saliva and other 

 fluids. The changes are, therefore, physical and chemical. The walls of 

 the rumen, by their contractions and resulting movements, may exert a 

 considerable amount of mechanical force on the aliments contained within 

 it, although this has been greatly exaggerated. Nothing like trituration 

 takes place, but simply thorough mixing of the new and old food together 



FIG. 153. STOMACH OF THE Ox. (Colin.) 



A, rumen (left hemisphere) ; B, rumen (right hemisphere) ; C, insertion of the oesophagus ; D, reticulum ; 

 E, omasum ; F, abomasum. 



and with fluid ; consequently, it is not necessarily the portion of food 

 which first enters the paunch which is the first to leave. The maceration 

 which the food undergoes in the fluids of the paunch is especially marked 

 in the case of grain and dry fodder, and is greatly assisted by the tem- 

 perature of the organ. 



The fluids contained in the rumen consist, in a great part, of water 

 which has been drunk and a large quantity of saliva, which is swallowed 

 with the first mastication and in the intervals of the act of rumination. 

 The rumen has, however, no secretion of its own, since no secretory 

 glands are found in its walls. Its reaction, as already stated, is generally 



