340 VETERINARY PHYSIOLOGY 



cellulose and probably also the pentosans, breaking them 

 down to various organic acids, chiefly acetic and butyric. 

 These combine with the bases of the alkaline saliva. The 

 resulting salts are absorbed from the intestine and are sources 

 of energy. In the upper part of the rumen the contents 

 may be acid from the accumulation of these organic acids. 

 The gases, methane, carbon dioxide, and in small quantities 

 hydrogen, are produced and excreted in the breath. The 

 process is therefore largely a destructive fermentation. It is 

 estimated that about 60 per cent, of the cellulose of the food 

 is disintregated in the rumen. As the cellulose is broken 

 down the cell contents are liberated and rendered accessible to 

 the digestive juices of the following parts of the digestive tract. 



In addition to cellulose, starch and sucfars undergo 

 destructive fermentation. It has been shown that the 

 addition of starch to a fixed diet leads to a corresponding 

 increase in the excretion of methane. 



Nitrogenous material is also broken down by bacteria, 

 and used to build up the proteins of their own protoplasm. 

 It seems that the soluble non-protein compounds are more 

 readily utilised than the proteins. When a plentiful supply 

 of soluble nitrogen is available, the multiplication and activity 

 of bacteria is increased, and consequently there occurs a more 

 extensive disintegration of cellulose. 



It has been suggested that the protoplasm of bacteria, 

 which are carried on into the stomach, is digested, and the 

 resulting products absorbed, and that it is by the bacteria 

 consuming the non-protein nitrogenous material and then 

 being themselves digested that non-protein nitrogen is made 

 available. Whether bacterial protein can be hj^drolysed by 

 the digestive enzymes is disputed. As the non-protein 

 nitrogenous material consists chiefly of amino-acids and 

 amides — the normal cleavage products of digestion (p. 320) 

 — it seems unnecessary to involve the aid of bacteria for their 

 utilisation. 



Stomach. — After being triturated between the leaves of 

 the omasum, the food enters the abomasum or true stomach. 

 The course of events in the stomach has been studied by 

 making a Pavlov's pouch in the goat. 



