1. As a result of soaking in water at body temperature (38° C), foods show variations in swelling ranging from approximately 10 per cent. to 260 per cent.2. The volumes of equal weights of different foods after soaking also vary within wide limits. The percentages of moisture in the soaked foods show corresponding variations, being in some cases as high as those found in roots or green fodder.3. These facts have led the authors to put forward a new conception of “bulk” in assessing the value of a ration.4. Feeding experiments have been carried out to determine how far this factor of bulk is applicable in practice.5. In the case of pigs of 40 to 80 lb. live weight, the bulk occupied by the foods did affect the quantity of food taken.6. With calves, the swelling capacity of the concentrated food did not yield any definite results so far as food consumption was concerned.