One of the essential constituents of every living cell is potassium, and this element is seized upon by the cells in the quantities necessary for their correct functioning. The fluids of the body, on the other hand, display an affinity for sodium, the plasma of the blood having a special preference for it. Herbivorous animals crave for common salt, whereas carnivorous animals strongly object to it.

Vegetable foods are rich in potassium, in contradistinction to animal foods, which are deficient in it. This liking of the herbivorous animal for common salt is explained by the preponderance of potassium salts in vegetable foods, for when the latter are absorbed into the blood a reaction takes place between them and the common salt there. The double decomposition results in the formation of chloride of potassium and sodium carbonate, which are rapidly ejected by the kidneys, thus depleting the blood of chlorine and sodium. Hence, the final result of the ingestion of vegetable foods is a craving for sodium chloride. It is said to be proved that when a man lives on animal foods he desires no common salt, but the moment he adds the potassium-containing vegetables, his affection for common salt begins, and it is remarkable that this is the only foreign salt which he adds in a chemical form to his food.

Bunge asserts that he has proved his theory by experiment, for he administered in three doses 18 grams of K2O to a man on a uniform diet, with a consequent loss of 6 grams NaCl and 2 grams of sodium, the potash salts having effected an exchange not only with chloride of sodium but also with the albuminate, carbonate, and phosphate of sodium. He estimates that if a man lived entirely on a diet of potatoes he would consume 40 grams of potash salts, whereas if he employed rice as his sole diet and took enough to supply him with 100 grams of protein, he would only obtain 1 gram of potash salts. Hence the necessity for eating salt with potatoes.

He considers, however, that vegetarians may be able to live without adding common salt to their dietary, but they would have a very strong disinclination to eat potatoes. Whatever truth there may be in the theoretical part of this argument, however, it is a fact that amongst vegetarians and fruitarians are to be found the strongest supporters of the salt-free diet. In Battle Creek Sanitarium the patients are encouraged to subsist without the addition of salt at the table, and comparatively little is added in the kitchen. It may be that special methods of cooking vegetables rich in potassium salts, e.g., potatoes, beans, peas, etc, are in vogue, but an effort is made to create a fondness for foods like rice, which is almost free from alkaline salts. It is recognised that this entails much less excretory work on the kidneys, and on this point Bunge has shown that on a diet of meat and bread without added salt 6-8 grams of alkaline salts will be excreted in twenty-four hours; on a diet of potatoes and salt, 100 grams will be excreted in the same time; whereas where rice is the staple article of diet only 2 grams of alkaline salts are excreted each day. Chlorine in the body is always to be found in the inorganic form, and probably an average man of 70 kilograms will contain nearer 150 grams than 200. The five litres of blood should account for about 25 grams, while 40 grams will be found in the 35 kilograms of muscles: the fat and bones contain still further smaller proportions.

Chloride of sodium may be withdrawn from the body -

(1) Daring fasting and underfeeding; e.g., Cetti excreted in ten days of his fast 175 grams.

(2) By the administration of large quantities of the alkaline carbonates or compounds of the alkalis with vegetable acids,

In such circumstances not only chlorides of sodium and potassium, but other acid substances are excreted.

(3) By frequent vomiting or by frequent washing out of the stomach. By this means the alkalinity of the blood can be temporarily raised, but this condition only lasts for a very short time, as the body rapidly absorbs more chlorine.

Chlorine can be replaced in the body by bromine, but not by iodine, and in certain circumstances it is possible to find in the stomach hydrobromic acid instead of the usual hydrochloric acid.

From 3 to 4 grams of phosphoric acid (P2O5) are required each day by the body. It differs from chlorine in this respect, that whereas the latter can be retained on occasion, phosphoric acid continues to be excreted even during starvation. When, however, flesh is put on, a certain amount both of nitrogen and phosphoric acid is stored up in the tissues in the definite proportion of 16.7:: 1, and a still larger supply is required both for the growth and repair of the bones. A certain amount of organic phosphoric acid is absolutely required by the tissues, although they can very well exist without any inorganic supply.

Lime in the form of carbonate can for a time be stored up in the body in large quantities. For every gram of lime, bone will be found to contain .73 gram P2O5 and flesh .137 gram P2O5. Three-quarters of a gram of magnesia (MgO) are required by the body each day.

It is quite certain that mineral salts are of vital importance to the body, as experiments on animals with food depleted of its salts speedily terminate in death. Chittenden holds strong views upon this subject, and this will be again referred to later on, when dealing with his low protein theory, but it may be stated here that he believes that protein pure and simple is unlikely to be utilised as a food in the body except in association with some salt of sodium, potassium, or calcium. The freedom from scurvy when fresh food or lemon-juice is administered is closely associated with this problem of the dietetic necessity for mineral salts.

Wright attributes many troubles to the diminution of calcium in the blood, amongst them chilblains: non-salt-eaters are said to suffer severely from this irritating affection, On the other hand, the non-salt-eaters contend that this is not so, and that they are never afflicted with eczema, influenza, rheumatism, colds in the head, even when they discard woollen underclothing, and that they gradually regain the faculty for distinguishing the delicate natural flavour of foods. We shall revert to this subject later on.

Mendel and Stanley Benedict have made a series of investigations into the paths of excretion for inorganic salts, and the following are among their conclusions. When soluble magnesium compounds are introduced into animals parenterally (i.e., by other channels than the alimentary canal), the greater portion not absorbed by tissue leaves the body by way of the kidneys in less than forty-eight hours. This is accompanied by a diminished output of calcium by the faeces, and an increased excretion by the kidneys, showing that the calcium content of the blood is increased. It is remarkable that the magnesium introduced in the manner mentioned never causes purgation - contrary to the usually accepted opinion. The body has the power of storing both calcium and magnesium, thus introduced, for a period of several days. The one base is capable of partially replacing the other, although this vicarious action is not sufficient to account for the common prescription of magnesium salts in oxaluria.