In the dietetic theories we have already discussed, our attention has been riveted mainly on the three essential alimentary principles, and each theory has been concerned with the disposition, from its author's point of view, of these items in the most effective proportions. It has been generally assumed that when the correct amounts respectively of protein, fat, and carbohydrate have been ascertained and the appropriate kind of protein has been settled, the foods which it is decided should be used as nutrients will contain all the mineral salts that are required. Even when it was demonstrated that such calamitous diseases as scurvy were more or less dependent upon the saline content of the food and were perfectly amenable to treatment by the addition of lemon-juice to the dietary, little heed was paid to the role of mineral salts in dietetics.

This is, however, hardly calculated to excite much surprise when we reflect on the enormous difficulties likely to be encountered in the course of such investigation, considering how little we know with absolute certainty of metabolism within the individual cells, of the term of existence of any single cell, or the length of time its bioplasm may persist. Much ingenuity and patient research have been displayed in tracing the proteins, fats, and carbohydrates through their manifold transformations till they find a home in the tissues or are utilised as sources for the production of energy, and we recognise that the term "food" must be held to embrace not only energy-producing substances, but anything that can enter into the composition of the cells. For this reason both water and the mineral salts must receive the designation of foods, and although the necessity of a constant supply of the former is obvious, constant renewal of the latter might at first sight be considered less compulsory, as the possibility of using anew the salts liberated from the waste material of the cells must be borne in mind.

Indispensability Of The Mineral Salts

Many experiments have been devised to illustrate the indispensability of the mineral salts in nutrition. Forster fed two dogs on fat, starch, sugar, and meat left over from the preparation of Liebig's Extract of Beef, this residue having been repeatedly boiled with water until it only contained .8 gram of ash for every 100 grams of dry substance, with the result that the animals died sooner than if they had been starved to death. Pigeons fed with casein and starch met a similar fate. Bunge suggested that the fatal termination of the experiment was not due directly to lack of salts, but indirectly, because the sulphuric acid due to the katabolism of tissue protein extracted alkalis from the cells and so produced their disruption. Even with less ash in the food he argued that were a sufficient supply of alkali to unite with the sulphuric acid administered, then death should at least be delayed. The experiments were accordingly repeated by Lunin, with the addition of various alkaline salts, and the proposition was found to be accurate. Nevertheless, it was proved in the case of mice, at any rate, that life cannot be sustained without the addition of salts to the food, and that even by adding artificial salts the inevitable result was only delayed a short time.

Much other evidence exists to demonstrate that although mineral salts are unable to furnish the body with energy they are quite as important in nutrition as the better known foodstuffs, and that they subserve many complex functions in the economy. The proteins, fats, and carbohydrates may be regarded as the rank and file of nutritive substances, while the mineral salts are the executive officials responsible for the accomplishment of effective work; but it is less easy to ascertain the exact proportionate quantities necessary for functional efficiency than it is to officer a military unit. In the absence of research and accurate information, irresponsible theorists have occupied the ground with misleading conceptions, but happily these are fast vanishing in the face of the renewed attention given by physiologists to the subject.

Erroneous Views Of Unscientific Writers

There are many lay writers on dietetics who have promulgated the view that all disordered conditions of the blood are due to an excess of salts in the food, and particularly to an excess of acid salts. In considering the uric acid theory I pointed out how frequently the inclusion of some highly acid fruit in a meal will determine an attack of rheumatism, and the conception just mentioned is simply a reflex of the urid acid theory that the body is capable of storing up somewhere in the tissues its acid waste matters. There is, of course, no physico-chemical evidence of this, while there are many facts which point to a contrary conclusion.

Chloride of sodium is especially blamed for being a "retentive of uric acid," but all the other salts, natural or otherwise, are looked upon with grave suspicion. Hence on the grounds that they are neutral, starchy foods are commended in preference to meats to all invalids or delicate people, but strong people are counselled to adhere to them for the purpose of helping to expel their stored-up acids, and it is even claimed that these foods have the faculty of neutralising such acids in the system. It is easy to recognise in this statement the theory that carbohydrates are the most suitable foods for those suffering from hyperchlorhydria, ignoring or oblivious of the other theory that proteins exclusively are the correct aliment, because they combine with the free acid, and entirely forgetful of the fact that a preponderance of starchy food may quite as easily lead to the production of organic acids, such as lactic, acetic, etc.

Sodium Salts

It is opportune here to take cognisance of the fact that chloride of sodium is a most important factor in the production of hydrochloric acid in the stomach, and it has always been a puzzling problem to account for the formation of a free acid from the alkaline blood and lymph. Maly's theory is, perhaps, the most satisfactory explanation and can be easily understood by a short study of the following formula: -

NaH2PO4 + NaCl = Na2HPO4 + HC1, i.e., the action of sodium dihydrogen phosphate upon chloride of sodium produces disodium hydrogen phosphate and hydrochloric acid. In all probability the sodium dihydrogen phosphate is itself derived from the action of the disodium hydrogen phosphate and the carbonic acid of the blood in this fashion -

Na2HPO4 + CO2 + H2O - NaHCO3 + NaH2PO4.

It is evident, therefore, that restriction of the consumption of chloride of sodium is an element of considerable importance in the cure of hyperchlorhydria.

Sodium salts are usually regarded as being much less depressant than the corresponding salts of potassium, but they are looked upon with some suspicion, in common with those of potash, in the treatment of gout. Falkenstein treats this disease by large doses of hydrochloric acid taken as acidulated water during meals. In his recent work he quotes the experiments made upon rabbits by Von Loghen, in which artificial gouty foci were made by injecting a solution of uric acid, after which some of the animals were treated by hydrochloric acid and some by alkalis administered by the mouth. They were then killed, and upon examination it was found that in those treated by alkalis the uric acid had been converted into urate of soda and the deposits were surrounded by a considerable amount of inflammation, whereas in those treated by acid the uric acid was unchanged and no irritation was evident. This, however, as also the new method of treating disease by sea water injections, encroaches rather on the domain of therapeutics, although not without dietetic significance.

Less equivocal and more decidedly related to our special sphere is Pavlov's observation of the inhibitory influence of the alkalis on the digestive glands, entirely controverting the doctrine that alkalis administered before a meal have the power to stimulate a flow of gastric juice. This erroneous belief was apparently fostered by omitting to take into consideration the stimulating effect of water itself, with reference both to the gastric and pancreatic juices, and also failing to note that hypersecretion is an accompaniment of most functional disorders of the stomach.