It has already been described how, by appropriately planned diets it is possible to prepare young rats so that there is no calcium phosphate deposited in the zone of primary calcification of the bones, and that when this is brought about by deficiency of phosphorus, of fat-soluble A and antirachitic substance, together with a moderate excess over the optimal of calcium in the diet, the administration of cod liver oil during a period of a few days leads to the deposition of a fine line of calcium salts across the uncalcified region in the epiphysis of the bone. This sudden calcification is due to the effect of the organic nutritive substance which is abundant in cod liver oil, but essentially lacking in many of our common foods. It was reasoned by Shipley, Park, Simmonds and Mc-Collum (30), that if by some means a disintegration of body protoplasm could be suddenly brought about, this might result in the liberation into the body fluids, from the destroyed protoplasm, the organic factors, calcium and phosphorus, and might make possible a deposition of calcium phosphate such as is seen in healing rickets. It seemed probable that a period of fasting would bring about a sufficient demand upon the body structures to bring about this result. A trial showed that this result is obtained.