The fermentation of cellulose in vitro by organisms from the rumen of sheep

The suggestion that micro-organisms are responsible for the decomposition of cellulose in the alimentary canal (Wildt, 1874; Zuntz, 1879; Duclaux, 1882) arose from the proof (Henneberg & Stohmann, 1860-4) that it is, in fact, cellulose which disappears during the pa#sage of crude fibre through the animal (Haubner, 1855).Tappeiner (1882, 1883, 1884, 1888), who was the first to investigate the fate of cellulose, found that paper pulp and cotton wool, when incubated under anaerobic conditions with the fluid contents of the rumen, dissolved slowly with the evolution of methane and carbon dioxide and the formation of fatty acids.He ascribed little nutritional value to the fatty acids, however, and suggested that the fermentation of cellulose was important only because it allowed the digestive enzymes access to the contents of the plant cells (Tappeiner, 1884).This view was not accepted (Henneberg & Stohmann, 1885); the fact that only traces of fatty acids appear in the excreta (Wilsing, 1885; von Knieriem, 1885) implies at least that they are absorbed and oxidized.There was already positive evidence of the nutritional value of cellulose (von Knieriem, 1885; Lehmann, 1889).Apart from the investigations of Markoff (1911, 1913) which added little to the information provided by Tap- peiner (1884) this aspect of ruminant digestion was abandoned in a state of considerable confusion.Tappeiner (1888) distilled the medium from somewhat prolonged in vitro fermentation of cellulose by rumen contentis, and from the combining capacity and composition of the silver salts of the mixed volatile fatty acids in the distillate, claimed that acetic and butyrio acids were the main products of fermentation.Quite apart from the possibility that his cultures had been qualitatively affected b'y the environment in which the fermentations were carried out, the chemical methods upon which the claim was based were not capable of distinguishing between mixtures of these two acids and any combination of the lower homo- logues.Examination of his data reveals no sound reason for the conclusion that only the 2-C and 4-C acids were among the products.On the occasion when he examined a series of fractions collected during progressive distillation Tappeiner (1884, p. 91) concluded, 'Zweifelhaft bleibt das Vorkommen von Propionsaure'.His data clearly indicated the presence of considerable quantities of propionic acid.Markoff's cultures also were probably subject to environ- mental alteration, and apparently he was unaware that the * The experiments were carried out in part at the Bio- chemical Laboratory, Cambridge, during 1937