THE FLUCTUATION OF pR AND ORGANIC ACIDS IN THE RUMEN OF THE SHEEP

It has long been known that bacterial fermentation of cellulose in the rumen is associated with the production of a mixture of lower fatty acids, methane and carbon dioxide. It was first shown by Pringsheim (1912) and later confirmed by Woodman & Stewart (1928) that the addition of toluene to thermophilic cultures of cellulose-splitting bacteria resulted in the accumulation of glucose, and Woodman (1930) suggested that glucose was the product that was of nutritional value to the animal. Broadly speaking, theories regarding digestion of cellulose fall into two categories; those that emphasize the importance of the chemical products of fermentation, glucose and the lower fatty acids, and those that regard the food eaten by the animal as a substrate upon which the organisms of the rumen thrive, the bacteria and Protozoa forming the end-product which is subsequently digested by the sheep. Pochon (1935, 1938) put forward an ingenious explanation which belongs to the first school of thought; he isolated a cellulose-splitting organism which he named Plectridiwn cellulolytiam from the rumen of the ox and found that if the pH of the medium in which active cellulose fermentation was proceeding was reduced to 4, glucose accumulated. This change is similar to that which occurs when ingesta pass from the rumen to the abomasum, and he suggests that glucose is formed in the abomasum of the animal and the lower fatty acids that are formed in the rumen are waste products. Baker (1939) supports the second theory. He studied the decomposition of plant tissue microscopically with the use of polarized light and was able to observe the breakdown of cellulose by the loss of double refraction in the cell walls. Bacteria were intimately related to the areas where erosion was occurring and these organisms were iodophilic. He considers that the bacteria besides exerting cytoclastic activity take up the sugars formed by hydrolysis of cellulose and so protect them from further degradation. These sugars are condensed to an amylodextrin type of polysaccharide and so produce the blue staining reaction with iodine. The bacteria are subsequently digested by the ruminant either before or after ingestion by the ciliates of the rumen.