In a previous publication1 we gave the results of some experiments on the iron reserve in animals, first as affected by the standard casein diet, and second as affected by the feeding of food known to be rich in available iron. While it is commonly stated that the body does not have any reserve of iron in the same sense that it has reserves of calcium and phosphorus, there are many clinical facts which make it seem likely that there must be at least enough iron in reserve to take care of the ordinary contingencies of everyday life. Relatively prompt recovery of animals and human beings after bleeding, even when the iron in the diet is not especially abundant, would seem to make this point apparent. The experiments referred to were undertaken with the idea of determining in a positive manner whether this surmise is correct, and whether an iron