of energy as well as their function in the repair of and in constructing tissue. The mineral salts are of importance as tissue builders. Their chemical changes taking place in the body are not attended by any liberation of heat or energy-at least, not of enough importance to be considered here. This does not mean that they do not exercise important functions in the human economy.

Function of Salts in the Body.--In studying the subject of osmosis and diffusion, we learned that they maintain the normal composition of the body fluids by regulating the osmotic pressure, and so playing an important rôle in the control of the flow of water to and from the tissues. For the body consists largely of water, which is an essential element for the removal of effete products arising from the various processes of metabolism, cell growth and disintegration.

According to Howell (4) these inorganic salts constitute an essential part of the composition of all living matter. They are an integral part of the structure of the living molecule, and are vitally necessary to its normal reactions or irritability. "Even the proteins of the body fluids contain definite amounts of ash, and if this ash is removed, their properties are seriously altered, as is shown by the fact that ash-free native proteins lose their property of coagulation by heat. The globulins are precipitated from their solutions when the salts are removed." The special importance of the calcium salts in the curdling of milk receives attention in the section dealing with this foodstuff. The action of the salts of iron in the production of hemoglobin has received attention elsewhere. It is an accepted fact that all the salts of the body possess no nutritive value. Year by year our conception of the metabolism of the mineral constituents of the body broadens and "the time will doubtless come when the special importance of the potassium, sodium, calcium and magnesium will be understood as well, at least, as we now understand the significance of iron, and quite possibly this knowledge will find a direct therapeutic application, just as in the case of iron" (5).

According to the teachings of Bunge the proteins contain from 0.5 to 1.5 per cent of sulphur, which during metabolism is transformed into sulphuric acid. Under normal metabolic conditions, the sulphuric acid arising in this manner combines with the inorganic salts contained in animal or vegetable foods. The acid, being neutralized, is removed from the body by the organs of excretion. If there are no salts or bases at hand to neutralize the acid so evolved, it seizes upon the salts or bases of the body tissues, and, as has been picturesquely said, it wrenches from their places the bricks of the structure, thus bringing about a catabolic destruction of

the organism. This statement may be met by a description of the protective agency of the organism in its ability to split off ammonia from the nitrogenous organic compounds, thus neutralizing the injurious effect of free acids. But this power has its limitations. Furthermore, it is not certain that ammonia is always present in these special cells from which the sulphuric acid originates to start its catabolic process (6). Lunin writing on this subject coincides with the views of Bunge. In a series of experiments he fed animals on practically an ash-free diet, adding only enough sodium carbonate to neutralize acidity. They were kept viable twice as long as the control animals subsisting on the same food, minus the sodium carbonate. Sodium chlorid did not answer the same purpose, nor did the carbonate of the same base indefinitely prolong life, death eventually resulting from the want of the proper inorganic salts in the food. The haphazard addition of mineral substances to the ration will not satisfy the system. Animals fed with normal milk will live, but the same animals will die when given an artificial milk even though it contains the exact percentage of casein, fat, sugar and the salts of milk. The reason is not explainable, though it is probable that the mineral constituents of normal milk are chemically combined with its inorganic constituents. It is known that the ions of inorganic materials enter into combination with protein. We may assume, too, that at least some of the inorganic constituents of foodstuffs form with organic substances a loose combination, thus influencing the assimilation and value of the latter.

Sodium chlorid, calcium and the ferrugenous salts are of special importance to the organism. Sodium chlorid occupies a peculiar place among the inorganic constituents of our diet, and according to Howell (7) it is the only one which we deliberately add to our food. The other inorganic material is taken unconsciously in our diet-but although sodium chlorid exists also in our food in relatively large quantities, we purposely add more. Bunge has pointed out "that among men and animals the desire for salt is limited, for the most part, to those who partake largely of vegetable food. This writer also calls attention to the fact that in the use of a strictly animal diet, craving for salt is not felt. In the use of vegetable diet, on the other hand, the craving for salt becomes so marked as to constitute a serious inconvenience when for any reason it cannot be added to the diet. It may be that this longing for salt by vegetarians is governed by the high percentage of potassium salts in all vegetables, the potassium salts reacting with sodium chlorid during the process of digestion. For, as Howell says, potassium sulphate added to the blood reacts with sodium chlorid, resulting in the formation of

potassium chlorid and sodium sulphate. These two salts, except in negligible quantities, being foreign to the blood, will be excreted by the kidneys, thus the blood will lose some of its sodium chlorid (8).

The subject of salt-poor and salt-free diets is discussed at length in the following volume of this work. It cannot be doubted but that we habitually, under ordinary conditions, use sodium chlorid in much larger amounts than is necessary to maintain the normal sodium chlorid content of the blood. Its universal use, as a condiment by all classes, unconsciously leads to the habit of using it in excess of normal requirements. The continuous ingestion of excessive quantities of sodium chlorid will eventually produce a condition of anasarca, owing to the fact that the physiological action of the salt increases osmotic pressure in the tissues. Likewise in conditions of edema or of "water-logged" conditions the restriction of table salt from the foods will give a contrary result and aid in the restoration of the parts to a normal condition, so far as the water in the tissues is concerned.

The importance of the calcium salts has been clearly demonstrated by feeding experiments. Howell concludes that when young dogs are given a diet poor in calcium salts, they fall into a condition closely resembling rickets in children, owing to deficient growth of the bones. Pigeons when fed on a calcium-free diet, soon exhibit a condition of atrophy and fragility of the bones due in all probability to the lack of calcium in the food. As in the case of other food materials, there must be maintained a calcium metabolism in the body. There is some evidence that the calcium content of the body increases with age, as the bones are exceedingly brittle in the aged, and become more fragile and more liable to break than in youth, and furthermore, in advanced life elasticity of the arteries diminishes as the calcium salts are deposited in their walls.

The ferruginous salts are constantly necessary for the production of new hemoglobin; the requisite amount is supplied normally in our food in which they exist in organic combination. (See analysis of iron content of various foods in a subsequent page of this chapter.)

The uses of the mineral salts derived from food have been summarized by Thompson as follows:

1. To regulate the specific gravity of the blood and other fluids of the body.

2. To regulate the chemical reaction of the blood and the various secretions and excretions.

1 Volume II, chapter on Scientific Feeding.

3. To preserve the tissues from disorganization and putrefaction. 4. To control the rate of absorption by osmosis.

5. To enter into the permanent composition of certain structures, especially the bones and teeth.

6. To enable the blood to hold certain materials in solution.

7. To serve special purposes, such, for example, as the influence of sodium chlorid on hydrochloric acid formation, and that of lime salts in favoring coagulation of the blood.

MINERAL CONTENT IN FOODS

Calcium.—We will now pass on to the consideration of the amount and kind of mineral salts met with in different articles of food and will first take up calcium, because it is one of the important salts of the body. The following table by Hoobler (9) shows the calcium percentage in the following foods:

CALCIUM-CONTAINING FOODS WITH CONTENT ESTIMATED AS CaO

Fruits, 30 to 7 per cent.-Citron, oranges, pineapples, figs, pears, cherries, olives. Berries, 14 to 8 per cent.-Strawberries, gooseberries, currants, huckleberries. Nuts, 9 to 8 per cent.-Almonds, walnuts.

Cereals, 8 to 7 per cent.-Oatmeal, cornmeal, wheat flour.

Vegetables, 27 to 5 per cent.-Savoy cabbage, cauliflower, onions, lettuce, radishes, celery, cabbage, endive, spinach, asparagus, carrots, kohlrabi, turnips, rhubarb, artichokes, pumpkin, lentils, cucumbers, tomatoes, beans.

Milk, eggs, cheese, 35 to 8 per cent.-Cheese, milk, egg yolks, eggs.
Meat and fish, 18 to 7 per cent.-Oysters, salmon, pickerel, pork.

Magnesium. We will next consider magnesium, which is usually present in foodstuffs in about the same proportion as calcium. There are, however, exceptions to the rule. In milk, for instance, magnesium is less, while in meats it is rather more abundant than calcium, and in bread there is actually five times as much of the former as the latter. The following table from Hoobler gives the magnesium content of the following foods.

MAGNESIUM-CONTAINING FOODS WITH CONTENT ESTIMATED AS MGO

Fruits, 8 to 5 per cent.-Apples, pineapples, oranges, figs, pears, citron, cherries, plums.

Berries, 6 to 5 per cent.-Currants, huckleberries, gooseberries.

Nuts, 18 to 6 per cent.-Almonds, walnuts, chestnuts, cocoanuts.

Vegetables, 9 to 5 per cent.-Tomatoes, sugar beets, peas, cauliflower, kohlrabi, lettuce, spinach, celery, carrots, onions.

Cereals, 16 to 5 per cent.-Corn, cornmeal, wheat, wheat flour, barley, meal, buckwheat, rice, rice flour, rye flour, oatmeal, rolled oats, graham bread.

Meats and fish, 9 to 5 per cent.-Salmon, pork.

Iron.-Iron, although one of the most widely distributed elements, occurs in the uncombined state only in small quantities, and as such is of no use in organic nature. It occurs in the earth in combination with oxygen, and is taken up by plants as an inorganic oxid. There are two forms: ferric oxid, which is a weak base, unable to fix carbonic acid; and ferrous oxid, a strong base which forms neutral salts with all acids. Iron is of extreme value as a carrier of oxygen, especially in organic life. It is concerned in the production of chlorophyll; without it the plant becomes pale and etiolated. As a part of vegetables it is consumed by animals and utilized in the construction of hematogens (iron-containing compounds of nucleo-albumin) and hemoglobin (the oxygen carrier of the blood).

The most important inorganic salt to which the dietitian needs to give special attention is iron. This substance is absolutely essential in the making of rich red blood. In certain diseased conditions it sometimes happens that more iron is excreted from the body than is assimilated from the food. This disturbed metabolism is the result of some disturbance of nutrition either in the digestion, the absorption or the assimilation; but whatever the disturbance is, the blood-making organs do not receive the necessary amount of iron. The blood becomes nearly destitute of hemoglobin; the pallor of the patient becomes extreme, until it reaches a condition of waxy etiolation.

It is difficult to give precise figures as to the amount of iron present in different articles of diet. In animal foods it depends very largely on whether the animal was bled, or not, when killed. In vegetable foods it varies very greatly with the amount of iron in the soil.

Another source of iron is to be found in the chlorophyll or green pigment of plants and vegetables, usually served in the menu in the form of greens, as spinach, turnip tops, celery, cabbage and chard. It is interesting to note in passing that the highly colored, deep red meat of the better cuts of steak or mutton, or the breast of wild game, as well as the highly colored plant green, owes this coloring to a pigment rich in iron. The dietitian seeks this pigment to bring back to the blanched cheek of his anemic patient the ruddy flush of health, which is maintained by a blood rich in iron.