The quantity of iron contained in a man weighing 70 kilograms is calculated to be about 3.2 grams, and something like 7 to 8 milligrams are excreted daily by the intestine during fasting experiments on man. We may take it, therefore, that a diet containing 10 milligrams of iron should suffice to provide the daily requirements of the body for that substance, and this is the average content of an ordinary mixed diet. It is especially abundant in foods such as beef and yolk of egg, while a litre of milk only contains about 2.3 milligrams of iron, so that were the diet restricted to milk alone, quite 4 litres would be required to supply the necessary quantity of iron. The amount of iron in the body of a newly-born rabbit is greatest at the time of birth, and gradually decreases, until towards the end of lactation it is at a minimum, but the store is quickly replenished as soon as food richer in iron begins to be taken. An analogous state of affairs exists in the infant, and hence it is unwise to restrict the human offspring to a milk diet for a longer time than the eight or nine months of the ordinary period of lactation. In health, it is sufficient to provide the body with the amount of organic iron contained in an ordinary mixed diet to maintain the supply in a normal state of efficiency for the purposes of the organism, but whenever any marked deficiency of iron exists in the blood, then it is requisite to administer medicines either containing iron or other substance capable of stimulating the blood-forming organs to greater activity. This is necessary because there is no food with an iron-content sufficiently large to cause the disappearance of anaemia.

The ratio of sodium, chlorine, iron, and calcium to potassium and phosphoric acid required by animals is far higher than exists in most plants. This is well exemplified by the appearance of "bran rachitis" amongst horses fed largely on bran, the ash of which contains 3 per cent. of phosphorus pentoxide and only .2 per cent. of lime, and which is, therefore, unsuitable as a bone-forming food, despite a widespread belief to the contrary.