If food material is actually burned in a stove, ashes would be found just as from coal or wood; that is, the food would not be completely consumed. The ash is made up of mineral matter which does not readily unite with oxygen at ordinary temperatures. This mineral matter in our food would be largely iron, calcium, sodium, potassium, and magnesium, while chlorine would be driven off as a gas. All food sub-stances contain more or less of these minerals even though it may be only a trace; but because of them one group of foods in particular is especially valuable in the diet. This group is comprised of all fruits and vegetables. Besides being in themselves very watery and also being useful for their woody fiber, they are our chief source of mineral matter, unless we except milk, from which we obtain most of the much-needed calcium.

An average adult human body if burned would leave about seven pounds of ashes. This mineral matter, which makes up the bony structure of the body, enters into the nails, hair, and teeth, and also plays an important part in the functioning of the different organs and body fluids, must be provided in the food particularly during the period of growth. This is another reason for the importance of having plenty of fruits and vegetables and also milk in the diet, particularly in that of children.

Iron is needed to insure the proper functioning of the blood. Without it the blood is unable to absorb the oxygen taken into the lungs and to carry it to cells where it is needed to burn up the food. A patient who is lacking in iron is said to be anaemic. It is far better to keep up the necessary amount of iron by such foods as spinach and other greens, molasses, oatmeal, and eggs, than it is to give the patient iron tonics. In the one case the iron is in such combination with organic matter that it can be easily assimilated by the body, whereas in the tonic the iron is in inorganic combination and cannot be so well used.

Calcium is needed for bone structure and is to be obtained from milk more than from any other food. The necessary daily requirement for an adult is found in less than 1 1/4 pints of milk or in 2 1/2 ounces of cheese, whereas it would take more than 7 pounds of white flour to obtain it, or 21 pounds of beef, or 2 1/3 pounds of turnips, or 2 1/2 pounds of carrots. It is also needed by the body for certain fluids in combination with both sodium and magnesium.

Sodium is an essential constituent of the blood and other body fluids. It helps in the making of the hydrochloric acid of the stomach. We use common salt, which is sodium chloride, so plentifully on our food that there is no doubt about there being a sufficient amount in our diet.

Potassium, another of the necessary minerals to assist in the proper functioning of the body, is found in green vegetables and fruits together with magnesium. If other minerals are in sufficient amounts, these will be also.

It has been found through experimentation with animals that a diet made up of purified protein, carbohydrates, and fats, with minerals in proper proportion, does not maintain life and growth. By introducing one type of raw food after another into this chemically pure diet, it was found that in order to have normal growth, the animal must have two types of substances hitherto unknown. These substances have not as yet been isolated and so have not been given definite chemical names. They are popularly known as "vitamines," but this is not a scientific term. It is known, however, that one type of these food accessory substances is found in a few fats, such as butter fat, egg yolk, and cod-liver oil, in the organs of animals such as liver, kidney, and sweetbreads, and in the leaves of plants. It is known as "fat-soluble A" for lack of a better name. The other is more abundant and is present in all fruit, vegetables, and cereal grains, though it is lost in the highly milled products made from the grain where the endosperm alone is used. It is called "water-soluble B." Here again we have still another reason for the plentiful use of fruits and vegetables, and also for the use of the coarser cereal products.

It is perhaps difficult for the novice to distinguish between all these different types of food substances, but it is certainly easy to remember that the safest diet is a varied one. We will go into this more fully when we discuss the planning of meals.

"Vitamines"

Hydrogen

Oxygen

Carbon

Nitrogen

Sulphur

Phosphorus

Iron

Calcium

Sodium

Magnesium

Potassium

Chlorine

.............Water

..............Carbohydrates: starch, sugar, cellulose

..............Fats

..............Protein: meat, fish, milk, eggs, cheese;

............. pulses, nuts

............. Mineral matter or ash: fruits and vegetables