The specific gravity of individual particles of digesta may be of importance in determining :he length of time such particles remain in the reticulo-rumen (Schalk & Amadon, 1928; Magee, 1932) . This paper is an account of a short series of determinations of the specific gravity of such digesta made during a wider investigation on the importance of the rate of passage of foods as one of the factors affecting their digestibility and utilization (Balch, 1950). METHODS Samples of digesta were

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... ed from two cows with large rumen fistulas. Throughout the experiment the cows were being fed an ample all-hay diet. The rumen fistulas were closed by means of the cannula and bung described by Balch & Johnson After removal from the cow 2-4 hr. after feeding the samples of digesta were strained through cotton gauze stretched across a filter funnel of wide bore. It was found that the amount of liquid that drained from the digesta from the ventral sac was much greater than that draining from the digesta from the dorsal sac of the rumen. The specijic gravity of representative samples of digesta. The specific gravity of small samples of digesta from which free water had drained was determined by means of a specific-gravity bottle using kerosene (tractor vaporizing oil) of known specific gravity as the liquid to be displaced. The separation of particles of different specijic gravity in digesta. Four mixtures of kerosene and bromobenzene were prepared having specific gravities varying from 0.977 to 1.601. These values were first checked by hydrometer and varied slightly in the course of the experiments. About 200 ml. of each mixture were prepared. They were placed in 250 ml. measuring cylinders (internal diameter 3.7 cm.) and after about 10 g. digesta had been gradually added the cylinder was vigorously shaken and the contents stirred with a wire plunger. Several minutes were then allowed for separation of the particles, this process being aided by very gentle stirring. After separation, floating particles were skimmed off and those remaining were separated by filtration, both fractions being subsequently dried and weighed. By this means it was possible to calculate the percentage, by dry weight, of the digesta having a specific gravity greater or less than that of each of the four mixtures.