THE DIGESTION OF FOOD 101 



layer is covered with numerous leaf-like projections, in 

 which the blood vessels are freely distributed. During 

 its stay in this reservoir, where it is held for remastica- 

 tion, the moist food becomes thoroughy softened and 

 besides undergoes a variety of changes, chiefly those due 

 to bacterial ferments which probably bring about the 

 extensive digestion of the cellulose, estimated at from 60 

 to 70 per cent. These fermentations are attended by an 

 evolution of gases, which imder ordinary conditions are 

 absorbed into the blood current. It may be suggested 

 that hoven and the puffing up of the paunch of a 

 freshly-kiUed bovine are due to the partial or total failiu-e 

 of the blood to take up these gases. Sometimes unnatural 

 and dangerous fermentations set in, induced often by the 

 consumption in the spring of a large quantity of easily 

 fermentable food such as green clover. This causes hoven, 

 and unless the gas pressure is at once relieved by an 

 opening the animal often dies, due sometimes to the 

 bursting of the rumen. Some authorities claim that 

 proteolytic and amylolytic changes occur in the nmien 

 brought about not by enzyms secreted by the rumen but 

 by those contained in the food. 



140. The reticulum. — ^A portion of the food reaches 

 the reticulimi either through the esophageal sht when 

 first swallowed, or through a large opening between the 

 rinnen and the reticulum. That which goes directly to the 

 reticulum when swallowed is mostly fluid. The reticulum 

 also communicates with the third stomach by an opening. 

 This is the smallest division of the stomach, and derives 

 its common name from the fact that its interior surface 

 is divided by ridges of the mucous membrane into cells 

 which bear a close resemblance to a honeycomb. These 

 cells, which are several-sided and quite deep, appear to 



