Bunge (1889Bunge ( , 1892 realized that milk contained very little iron and he believed that animals which depended entirely upon it for some time after birth were born with a store of iron in their livers to tide them over the suckling period. These conclusions, which were based largely upon a study of the rabbit and the guinea-pig, had a great influence upon subsequent thought. Bunge (1892) found the rabbit, with a long suckling period, to have a large store of iron in the liver at birth; the guinea-pig, which is able to eat food other than milk from the first day onwards, had not. The essential points of his generalization were therefore: (a) milk is a negligible source of iron; (b) the liver contains enough iron at birth to supply the needs of the growing animal during suckling. It follows at once if the theory is true that suckling animals should have little if any more iron in their bodies at the end of suckling than they had at the beginning, and that unless the store is adequate a state of physiological 'anaemia' is inevitable towards the end of suckling.Fontes & Thivolle (1925 a, b) first showed that this theory required modification by demonstrating that the total amount of iron in puppies increased considerably during suckling, and concluded that the source of this iron was the milk. The increase in total body iron, moreover, was so much greater than the amount which the liver could have contributed to the rest of the body that the value of this 'store' to the puppy was clearly a relatively small one.