Rumen liquor contains a high concentration of potassium (Parthasarathy, 1952 a), and in view of the known effects of this ion on cell membranes it was considered desirable to study the effect of solutions containing potassium in concentrations comparable to those of the rumen liquor, on the absorption of other ions and, in particular, of fatty acids. There is very little information to be found on the absorption of inorganic ions or of water from the rumen. Masson & Phillipson (1951) noted that when solutions containing no chloride were introduced into the rumen chloride appeared and they concluded it came from the blood. Scarisbrick & Ewer (1951) have reported on the irregular behaviour of inorganic phosphorus in the rumen, while recently Sperber & Hyden (1952), on the basis of experiments in which they studied the behaviour of solutions containing potassium, sodium, chloride and phosphate in a 'Pavlov' pouch of the rumen of goats, suggested that the rumen is selectively permeable to inorganic ions.The question whether water is absorbed from the rumen has never received close attention and, as there are good reasons to believe that water is absorbed from the digesta before they reach the abomasum (Garton, 1951; Masson & Phillipson, 1952), particular attention has been given to the volume changes that have occurred during the course of these experiments. The results show clearly that the rumen epithelium is readily permeable to water, but further work is needed to establish the direction of the flow under normal conditions. Some evidence has been found to support the contention of Sperber & Hyden, but the support so far is qualified. No evidence has been obtained to show that fatty acid absorption is affected by the ions under investigation.
METHODSSheep previously fitted with an ebonite rumen cannula were used in all experiments, and the surgical techniques for the isolation and emptying of the rumen and for the withdrawal of blood are identical with those previously described (Masson & Phillipson, 1951 (McAnally, 1944) was added to the sample, as this prevents the appearance of chloride in the distillate. The modification of the McClendon procedure, the accuracy of which is given by Kiddle, Marshall & Phillipson (1951), was used for total volatile acid in blood. The freezing-point of rumen liquor and of blood serum was used as an indirect measure of the osmotic pressure of these fluids. The procedure described by Findlay (1932) was followed. Normally fed sheep fitted with rumen cannulae provided rumen liquor. The samples were drawn rapidly without suction, filtered rapidly through gauze and stored under liquid paraffin. Blood was withdrawn from the jugular vein by a syringe and transferred to a centrifuge tube under liquid paraffin. The serum so obtained was used for the determination of the freezing-point. The effect of loss of carbon dioxide or rumen liquor by exposure to the air was examined by determining the freezing-point after exposure and then again after re-equilibration with a mixture of 60% CO2...