376 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



alkaline, and is derived from the saliva. Occasionally, the reaction of 

 the rumen may be found to be acid. This may be due to fermentation 

 occurring in the contents of this organ, and is especially seen in nursing 

 calves, in animals fed on roots, and in cases of faulty digestion. It 

 nearly always occurs in animals fed on green fodder, where the conditions 

 are favorable to the fermentation of sugar. Occasionally, also, the reac- 

 tion of the rumen, which may be found to be acid after death, is due to 

 the regurgitation of the contents of the fourth stomach into the first 

 three compartments. In the rumen the conditions are especially favor- 

 able for the digestion of carbohydrates, for the conditions are favorable 

 for the action of saliva, which is thus enabled to convert starch into 

 sugar. Cellulose, also, is said to be digested in the rumen through fer- 

 mentative processes to as much as 60 to 70 per cent. Salts, sugar, muci- 

 lage, gum, and other soluble substances may be dissolved out of the food 

 while in the rumen, and so prepared for absorption. No peptonization, 

 however, occurs ; for all the various bases, salts, and albuminoids which 

 may be detected in the contents of this organ come solely from the food 

 and the secretions and liquids which have been swallowed, and not from 

 any secretion poured out by the rumen itself. The function of the rumen 

 is, therefore, simply to act as a reservoir, in which the food, after being 

 swallowed, is collected, undergoes maceration, and is again, from time to 

 time, returned to the mouth for a second mastication. In this organ the 

 food becomes softened, as the result of impregnation with liquids warmed 

 to the temperature of the body. 



The functional importance of the rumen is not equally marked at 

 all periods of life. This is especially seen in suckling animals, such as 

 calves, in whom the rumen is capable of containing one thousand one 

 hundred and seventy-five grammes, the reticulum one hundred, the 

 manyplies one hundred and sixty, while the cubic capacity of the 

 abomasum may amount to three thousand five hundred grammes (Colin). 

 Hence, digestion in the suckling ruminant is accomplished almost solely 

 by the fourth stomach, and the rumen does not acquire its great pro- 

 portionate size seen in the adult ruminant until the animal commences to 

 live on a solid vegetable diet. 



Although the reticulum may be regarded as an appendage to the 

 rumen, with which it communicates by a large opening, it also has a 

 special function to fulfill, which appears to be uniform in all ruminants. 

 It constantly contains fluid, since its base is on a much lower level than 

 the openings into the first and third stomachs. Fluid can, therefore, 

 only leave this compartment as a result of its own vigorous contractions, 

 such as precede the insertion of the cud into the oesophagus for rumi- 

 nation. 



The function of the oesophageal canal is to assist in the transfer of 



