deeding and l^igestion 



173 



lied out by the bacteria of the rumen, and the ciliates are commensals rather 

 than s\mbionts. "- The bacteria produce some sugar and large amounts of 

 volatile fatty acids, particularly acetic and propionic. ■''" At the peak of 

 digestion the rumen of a sheep may contain 6 to 9.7 gm. per cent of fatty acid, 

 compared with 0.269 gm. per cent in the dry food; these products of bacterial 

 action can be absorbed from the rumen, as shown by blood analyses."""' They 

 are also absorbed in lower regions of the digestive tract. In addition, any 

 organisms, bacteria or Protozoa, which pass into the abomasum or true stomach 

 are instantly killed by the acid medium and are then digested by the enzymes 



of the host animal. "^ In nonruminants, such as the horse, the caecum contains 

 a wealth of bacteria which break down cellulose; absorption from the caecum 

 seems not to have been studied. Even in man some hemicellulose '-^ and 

 pectin '" are digested by organisms of the large intestine, but it is assumed, 

 although not pro\ed. that the products are not absorbed. 



The rare occurrence of cellulases among animals may be correlated with the 

 rarity of ^-glucosidases. As shown in Tables 28 and 29, each animal which 

 has a cellulase probably has also a /:^-glucosidase, and animals which digest 



