Scurvy has been repeatedly ascribed to a deficiency in the potash salts of the food, producing a relative acidosis, but its etiology is still obscure and has been equally attributed to ptomaine poisoning and specific infection. Whatever its causation, however, it is known that a plentiful supply of fresh vegetables and of fresh meats cures the disease, and it is probable that potash is useful, less for its own sake than for the vegetable acids with which it is usually associated, and which by their oxidation induce a proper degree of alkalinity of the blood. It is important to remember the distinction between vegetable food-stuffs on the one hand and meat and cereals on the other. The characteristic of the former from our present point of view is an excess of base over mineral acid, and of the latter an excess of mineral acid over base, so that deprivation or insufficiency of vegetable foods tends to diminish the alkalinity of the blood and interfere with its power of coagulability. Wright has divided foods into three groups according to the reaction of their ash as determined after incineration: -

(1) Acid Foods

Barley, beef, eggs, maize, oats, rice, wheat.

(2) Neutral Foods

Animal fats, sugars, vegetable oils.

(3) Alkaline Foods

Beans, blood, carrot, lemon-juice, milk, onion, orange-juice, peas, potato, turnip.

The addition of a suitable proportion of fresh lime or orange juice, fresh fruit, fresh vegetable, fresh meat or beef-tea made from it, or fresh milk will cure scurvy, or, where tinned foods are being chiefly consumed, tend to delay or altogether prevent its onset.

Foods which are rich in potash almost necessarily require an addition of common salt, so that, as has been already explained, the excess of potash may be quickly eliminated. Bunge's conception, therefore, that common salt tends to widen the circle of our food supply is doubtless correct.

An interesting contribution - fraught with suggestiveness - has been made to our knowledge of the metabolism of the mineral salts by Motteram, who by careful spectroscopic examination has ascertained that the potassium-content of the red blood corpuscles of cancerous patients is considerably higher than in health, the difference being represented by the figures 1.5 and 3. The sodium-content, on the other hand, showed no change. The sodium.content of all cancerous tumours is the same, whereas the potassium-content of primary is higher than that of secondary tumours.

A comparison between the composition of the ash of milk and that of the young animal reared upon it shows a wonderful agreement except in the case of human beings. This striking difference is explained by the statement that it is essential for animals which develop very rapidly after birth to be nourished by a milk corresponding closely to the chemical composition of their young, whereas this is not necessary in the slowly developing human offspring, because the various tissues are not built up so uniformly, nor are so many changes taking place when suckling ceases and other sources of nutriment are resorted to. Lime Salts in Rickets. - A critical survey of the food of young children is closely bound up with the chemical composition of milk, and it is now recognised that in the past too much stress has been laid upon its content merely of protein, fat, and carbohydrate, and too little upon the amount of inorganic substances associated with them. From this point of view the most important salt is lime, which is absolutely indispensable for the growth of bones and teeth, and it has been suggested that rickets is caused by a lack of lime salts in the nourishment. Part of the routine treatment of this disease consists in the exhibition of phosphate of lime, on the assumption that there is a deficiency of lime in the food or drink, and this conception was, no doubt, fostered as much by the fact that rickets appear most frequently when for any reason there is a cessation in the administration of mother's milk as because its point of attack is chiefly centred on the bony structures.

In most cases, however, other parts of the body, such as muscles and nerves, are involved, and the osseous changes are frequently of slight significance, and it is known that rickets sometimes appears with a food that is rich in lime, and even when mother's milk is the sole item of nutriment. One great difficulty in the investigation has been the lack of knowledge as to the precise method of combination in which the inorganic substances are present in the food, whether as inorganic salts or closely incorporated with the proteins. Lime, we know, is present in milk in quantities proportional to the citric-acid-content, but it is not believed that the lime is simply dissolved by this acid. In any case it is fairly certain that all the lime is brought into a state of solution in the intestine and most probably absorbed by the duodenum, and so is capable of being assimilated.

It must be assumed, therefore, that deficiency of lime in the food is not the causative factor of rickets, but that the power of assimilation for lime is lessened. For this reason, in the treatment of this disease it is of greater importance to improve the metabolic powers by any means at our disposal than to increase the supply of lime.

There are bodily conditions, indeed, in which it may be judicious to exclude as far as possible foods containing lime, although the daily normal requirement of a child is no more than one-third of a gram, and that of an adult only a little over 1 gram. The view enunciated by dietists barely ten years ago, that it is exceedingly doubtful whether the intestine absorbs more mineral salts than the tissues require, has now been modified to the statement that the mineral matter of our food is absorbed in an excess far exceeding the physiological requirements of the body, but that the individual cells have a selective capacity enabling them to pick out from the mass presented to them the exact quantity essential for their perfect nutrition. Just how far this states the case with precision it is impossible at this time of day to say; but in the light of our knowledge of the occasional evil effects of an excess of chloride of sodium, it behoves us not to rest content simply when we have arranged for the provision of a supply of mineral salts which ordinarily suffices for nutrition.