When solutions of sodium acetate, propionate and butyrate are placed separately in the empty rumen of sheep anaesthetized with nembutal, analysis of the blood leaving the rumen shows that absorption of the acids occurs and that the rate of absorption appears to decrease as the molecular size increases (Barcroft, McAnally & Phillipson, 1944).. Recently this was reinvestigated by Gray (1948), who concluded that no absorption at all occurred from the rumen of sheep when the pH was slightly alkaline as would be expected when solutions of the sodium salts are introduced. Gray's method consisted of introducing solutions of sodium acetate and propionate into the empty washed rumen of an unanaesthetized sheep through a rumen cannula. Pectin was included in the solution as a marker. The solution was allowed to remain in the rumen for 5 hr. or more and was then removed and the interior of the organ was washed with water. The loss of pectin from the rumen was taken as indicative of the quantity of solution that had passed on to the abomasum; on this basis the quantity of acetate and propionate absorbed from the rumen was calculated and found to vary between -10 and + 22 m.equiv. during 5 or 6 hr. In addition, Gray (1948) introduced solutions of pectin or sodium acetate into the empty rumen of anaesthetized sheep from which the exits were blocked by ligature, and found a loss of less than 5 % of either substance over an experimental period of 4 hr.Acetic, propionic and butyric acids are absorbed more rapidly than the corresponding anions, and the rate at which free acid disappears from the rumen increases with the length of the hydrocarbon chain (Danielli, Hitchcock, Marshall & Phillipson, 1945;Gray, 1947). If the epithelium of the rumen is impermeable to the anion, as Gray (1948) contends, then the ratio propionic/ acetic and butyric/acetic should be greater in the blood leaving the rumen than in the rumen contents, but this is not so (Kiddle, Marshall & Phillipson, 1951); in fact, the mixture of acids in the blood leaving the rumen is much the same as that in the rumen except that it contains less butyrate. 190 M. J. MASSON AND A. T. PHILLIPSON On account of these contradictions a further series of experiments on the absorption of acetate, propionate and butyrate from the rumen has been conducted, and the results are recorded in this paper. METHODSChemical. Acetic, propionic and butyric acids were determined by steam distillation, after acidifying with sulphuric acid, using a 'Markham' still. The distillates were titrated with carbonfree 0-02 or 0-05N-potassium hydroxide under carbon-dioxide-free conditions using phenol red as indicator. In one experiment in which rumen liquor was used total volatile acid was determined in the same way after precipitation of protein by McAnally's reagent .Volatile acid in blood was determined by a modification of the method of McClendon (1944), the details and accuracy of which are described elsewhere (Kiddle et al. 1951).Chloride was determined in earlier experiments by the Volhard meth...

The digesta entering the abomasum of sheep consist of the residual products of the fermentations that proceed in the rumen and reticulum, which pass through the omasum to the abomasum where they are diluted and subjected to peptic digestion by the gastric juice secreted by the gastric glands of that viscus.

A technique for the galvanotropic separation of indigenous ciliate protozoa from the rumen contents of sheep is presented. A fractionation of these isolated protozoa into three populations—isotrichs, large oligotrichs, small oligotrichs—is described and illustrated. Some applications of these findings in rumen microbiology are enumerated.