A certain minimum amount of organic salts is essential to optimal growth. A further increase in these, even a great increase, does not further influence growth. Not only the total quantity of these salts, but also the quantities of the individual minerals and their mutual quantitative relationships are of decisive importance in regulating the assimilation of proteins.

If we are to have normal development the mineral elements in our diet must also be present in minimum quantities, but they must also represent proper ratios one to another. The mineral salts are most sensitive to any deficiency of any of them in the diet. Many common foodstuffs are deficient in iron and calcium, and these deficiencies reduce the ability of the body to assimilate the other elements. On the other hand, in experimental diets, any increase of one element raises the mineral requirements of all the others.

If health and development are to follow, certain relationships must prevail between the various salts. Berg, McCarrison, McCollum and others have amply demonstrated this. Rose found that a certain relationship must prevail between calcium and magnesium if the maximum development of the body is to be attained. Between lime and potassium, lime and sodium, potassium and magnesium and between the metals on the one hand and sulphur and phosphorus on the other, an optimum ratio exists.

The proper exploitation of both proteins and carbohydrates is determined by mineral metabolism, since they can be more readily oxidized in an alkaline medium than when an excess of acids is present. It has been repeatedly shown that an excess of bases over acid-forming foodstuffs ingested promotes the utilization of proteins. Zunts, of Berlin, showed that diabetics can more easily oxidize sugar if the body has an abundance of bases at its disposal. Abderhalden performed investigations which showed that a diet rich in bases is essential for the proper functioning of the hormones of the ductless glands.

Without iron there can be no oxygen supply for the cells. Without copper there can be no assimilation of iron. Without sodium there is no elimination of carbon-dioxide from the tissues of the body. Every physico-chemical process of the body is correlated with others and any failure in one spells a corresponding failure in the correlated processes.

May Mellanby says that the evidence shows that the calcium in the diet does not in itself directly control the calcification of the teeth, but that it is subservient to other dietetic factors. One of these is vitamin A. She thinks that she has demonstrated the existence of factors in some foods, particularly in cereals, and more especially in oats, that inhibit calcification. Phosphorus is as essential to the formation of good bones and teeth as is lime.

The present furore over vitamins has caused many ex-spurts to concentrate their whole attention upon these substances and almost forget the other elements of nutrition. We pick up a book or a magazine article or a report dealing with nutritional problems and we learn that a diet rich in vitamin A does thus and so, or a diet poor in vitamin B results in such and such effects. The minerals in the diets are particularly overlooked. Interest in vitamins is causing us to forget the importance of other food elements.

The present over-emphasis on vitamins is as absurd as if we were similarly to over-emphasize sodium, or magnesium. To ignore the organic salts, as is so often done in our mad rush for vitamins, is as foolish as would be the ignoring of the vitamins.

It has been demonstrated that regardless of the amount of vitamin A supplied in the diet, if some other constituent of the diet is wholly lacking, vitamin A can have no effect. Berg shows that on a cereal diet complete in A is without effect unless sodium and calcium are added to the diet in sufficient quantities to produce an excess of bases. McCollum and his co-workers have shown that when there is an abundance of vitamin A in the diet, the mother cannot secrete sufficient milk for her progeny, unless her food contains an adequate amount of organic salts in proper proportions.

The absence of anyone of the essential vitamins prevents the rest of them from functioning at all. If any one of them is present in but one-half or in but one-fourth the required amount, then the others, though abundantly present, will function only up to one-half or one-fourth of their full effectiveness.

Lack of vitamins disturbs calcium metabolism. A lack of calcium or an excess of calcium in the diet renders vitamin A of no effect. Vitamins are valuable only in the presence of each other. Calcium seems to be usable only in the presence of vitamin A.

McCarrison says that "in the absence of vitamins or in their inadequate supply, neither proteins, fats nor carbohydrates nor salts are properly utilized; some are largely wasted, while others yield products harmful to the organism. In such circumstances life may be sustained for a longer or shorter period, during which the body utilizes its stores of vitamins and sacrifices its less important tissues to this end. But there is a limit beyond which such stores cannot be drawn upon, and once this is reached the cells of higher function--secretory, endocrine and nerve cells--begin to lack vigor, and to depreciate in functional capacity, although the tissues may continue to hold considerable stores of vitamins. The disintegration process is delayed or hastened, lessened in severity in one direction or increased in severity in another, according to the character of their lack of balance."

There are many kinds of proteins and where one is securing his protein from one source only he is likely to suffer from protein inadequacy even though he is consuming an excessive amount of protein. The biological value of the various proteins varies considerably.

Proteins are broken down into their constituent ammo-acids in the process of digestion and these amino-acids are employed in constructing new and different proteins in the body, but amino-acids may be utilized by the body only to the extent that the diet supplies other protein constituents which enable the body to synthesize them into proteins proper to man. If more amino-acids are introduced into the blood than the presence of other elements will enable the body to utilize, the amino-acid content of the blood rises and there is an increased excretion of amino-acids in the urine.

It is at once apparent from this, that growth can proceed at an ideal rate only as rapidly as all of the essentials of growth become available to the growing organism.

It is found, in harmony with this law, that in the case of proteins, the value of a protein or mixture of proteins for structural purposes in the body, is limited if one of the indispensable amino-acids is deficient or wholly lacking. If and when this deficiency is remedied, a deficient supply of some other indispensable amino-acid constitutes a further limitation.