( Originally Published 1938 )
In addition to the elements derived from the proteins, carbohydrates and fats, the body is composed of mineral elements. The bones, for example, are made up of calcium and phosphorus. The brain, too, has a large amount of phosphorus. The blood contains iron and copper and the thyroid gland, iodine. All the tissues contain common salt which is known scientifically as sodium chloride.
Just like the other elements, these are constantly being broken down and excreted. Naturally they must be replaced. Therefore our food must contain them in appreciable amounts. This is imperative not only because they are needed for the building of bone, brain, blood and other tissue, but because they are necessary for other functions. They influence the irritability of the muscles, that is their power to react to stimuli. They also influence the acidity or alkalinity of the digestive juices, and maintain the neutrality of the body tissues the acid alkali balance to which we alluded when discussing the proteins.
Usually our diet contains enough of these elements for all purposes. Sometimes, however, as in the case of iodine in regions such as Switzerland where iodine is scarce in the water and soil, they are insufficient and cause serious bodily disturbances. The lack of iodine, for example, causes the simple goiter.
Most of our sodium chloride comes from the common table salt which we add to our food to make it more palatable, usually not realizing that our desire for it has a physiological foundation. It is particularly needed when doing severe muscular work or living in a hot climate. This is because a large amount of the body's supply of salt is given off in perspiration. English miners may lose a gallon of perspiration containing a quarter of a pound of salt during a day's work. They know from experience that they must eat raw salt as well as drink abundant water if they wish to feel comfortable. Most of them, however, prefer to take their supply of water and salt in form of beer and ale and usually rush off to a pub as soon as their work is finished.
Babies and growing children need more calcium than adults, but it is always needed. Foods vary considerably in their calcium content, although most vegetables contain calcium. The best source of calcium, however, is milk, and of course, cheese. The table of food values gives the amount of calcium, as well as the other minerals, in our common foods.
Phosphorus is very widely distributed in the normally healthy body. Indeed, it forms a part of the nuclei of the cells and is present in the bones and nervous system. It is found in such foods as egg-yolk, brain, lean beef, cheese, wheat, oatmeal, dried beans and nuts.
It is estimated that there is only about three grams of iron in the average adult and by far the largest part of it is in the hemoglobin of the blood. As small as this amount is, it is imperative that it be maintained because there is no reserve of iron in the body as there is a reserve of calcium in our bones. It is found in appreciable amounts in egg-yolk, dried beans, peas, oatmeal, wheat, prunes and many other common foods.
Iodine is found in every part of the body, but most of it 65 per cent, to be exact is found in the secretion of the thyroid gland. The amount of iodine in water and food varies, we said, from region to region. When the water is poor in iodine, it naturally is reflected in the food which was nourished by that water. This deficiency results in the enlargement of the thyroid gland. This is probably a compensation on the part of the gland, an effort to increase the number of cells that it may have enough cells to extract every bit of iodine from the food.
Iodine is found in grains such as wheat, oats, corn, barley, in carrots, salmon and in a highly nutritious food not eaten very much in this country goat's milk.