ACETIC ACID AND ACETATE 255 



cecum and colon: sheep (56 to 86 kg.), 7.9 to 9.1 g.; horse (458 to 662 kg.), 

 249 to 355 g.; pig (19 to 21 kg.), 2.3 to 8.7 g.; rabbit (approximately 1 

 kg.), 0.21 to 0.67 g. In the case of the sheep, the diverticulum of the 

 stomach, the rumen, and the reticulum contained from 26 to 91 g. of volatile 

 acids. The concentration of these acids was neghgible in the stomach of 

 the horse and rabbit, but small amounts were found in the stomach of the 

 pig, and greater concentrations in that of the sheep. In the latter animals, 

 the various parts of the gastrointestuial tract were found to have the 

 following volatile fatty acid content: rumen and reticulum, 6.0 to 9.7 g. 

 %; omasum, 1.1 to 2.1 g. %; abomasum, 0.1 to 0.2 g. %. Thus, the 

 volatile acids disappear from the ingesta before they pass into the glandular 

 portion of the stomach, namely, the abomasum. The concentration of 

 volatile acids has usually been found to be negligible in the small intestine. 

 It is believed that the \'olatile acids originate from the fermentation of 

 cellulose or of hemicellulose.^^ According to Gray and Pilgrim,^^ only a 

 small portion of the butja-ic acid arises directly from this fermentation. 

 Another fraction originates by synthesis of the acetate also produced, and 

 some may be derived from the protein fraction of the fodder. Moyle and 

 Baldwin ^^ demonstrated the presence of acetic, propionic, and butyric 

 acids, as well as of traces of formic acid, in the perienteric fluid of the 

 round-worm {Ascaris lumhricoides). An optically active 2-methylbutyric 

 acid was also found to be present. 



However, the low concentration of acetic acid in tissues other than those 

 of the gastrointestinal tract has been cited as e\'idence against the j8- 

 oxidation theory. ^^ Bloch^ is of the opinion that the failure to detect acetic 

 acid in the tissues is not an argument agamst the theory of its action as an 

 intermediate. The condition which must rather be satisfied, to establish 

 it as a metabolite lying on the main metabolic path, is the capacity of the 

 tissues to metabolize it as rapidly as it is formed. Under such circum- 

 stances, its concentration at any one time ^\dll not be relevant. There 

 are many commonly accepted intermediates in the catabolism of carbo- 

 hydrate or protein which are present in concentrations as low as that of 

 acetic acid; in spite of the fact that the demonstration of the former 

 compounds in normal tissues is not experimentally feasible, they have 

 been generally regarded as normal intermediates. 



One method for establishing the occurrence of a metabolite, which 

 ordinarily does not accumulate in sufficient amounts to permit analytical 



'3 F. V. Gray and A. F. Pilgrim, Nature, 170, 375-376 (1952). 

 i< V. Movie and E. Baldwin, Biochem. J., 51, 504-510 (1952). 

 i« W. C. Stadie, Physiol. Revs., 25, 395-441 (1945). 



