_Limitations_. The administration of food in the guise of medicine is sometimes advantageous; but medicinal foods are subject to the ordinary law of dietetics, and therefore cannot accomplish the wonders which are often claimed for them. The proprietary foods have been enormously overestimated, and have probably done more harm than good. The ultimate value of any food depends mainly on the amount of calories which it can yield, and on its supplying at least a minimum of proteins. In these respects, the medical foods are all inferior, for they cannot be administered practically in sufficient quantity to supply the needs of the body. They have a place as adjuvants to other foods, permitting the introduction of more food than the patient could otherwise be induced to take. Aside from the special diabetes foods and cod-liver oil, their value is largely psychic. _Predigested Foods_. The value of these is doubtful, for digestive disturbances involve the motor functions and absorption more commonly than the chemical functions. Their continued use often produces irritation. _Liquid Predigested Foods_. As sold, these are flavoured solutions containing small amounts (1/2-6 per cent) of predigested proteins, 1/2-15 per cent of sugars and other carbohydrates, with 12-19 per cent of alcohol, and often with large quantities (up to 30 per cent) of glycerin. Their protein content averages less than that of milk, and in energy value they are vastly inferior. Their daily dose yields but 55-300 calories including their alcohol; this is only one-thirtieth to one-fifth the minimum requirements of resting patients. To increase their dose to that required to maintain nutrition would mean the ingestion of an amount of alcohol equivalent to a pint of whisky per day. Of recent years very expensive preparations of real or alleged organic iron compounds have had a large sale. Iron is a component of haemoglobin, a solid constituent (13 per cent by weight) of the blood, which combines with the oxygen in the lungs, and is carried (as oxyhaemoglobin) all over the body, giving the oxygen up to the tissues. Haemoglobin is an exceedingly complex substance, but it contains only one-third per cent by weight of iron in organic form. The liver is the storehouse of iron, its reserve being depleted when there is an extraordinary demand for iron. The minute amounts of iron in ordinary food are amply sufficient for all our needs; any excess is simply stored, and, later excreted, and has no effect whatever on the circulating haemoglobin.