Normally, with a well-balanced diet, the organism receives adequate amounts of all the necessary elements through the food and water consumed. When, however, any one element is lacking, various diseases, sometimes very serious, may occur.
When soil lacks iodine, it is necessary to add it to the common salt. The water of the river Neva is considered to be the purest and the best drinking water in the world, but this purity is its main shortcoming. One of Leningrad water-works has begun to add fluorine to the drinking water since absence of fluorine frequently causes teeth trouble. What is more, Swedish scientists discovered that people who systematically use soft water are much more liable to develop cardiovascular diseases.
Some difficulties in supplying chemical elements to the organism arise because most substances composing the tissues and organs cannot be synthesized directly from elements. For instance, proteins are built up of different combinations of twenty-two amino acids, of which only ten can be synthesized by the organism, while the remaining twelve must be obtained ready-made. Besides, even when we ourselves produce the amino acids, the nitrogen necessary for the purpose must be supplied in the form of organic compounds. The same is true of glucose which cannot be synthesized directly from carbon and hydrogen in the organisms of animals, and this is why ready-made hydrocarbons are used to produce it.
Of the many substances which are absolutely essential to the organism, even in small amounts, mention must be made of vitamins. They are indispensable to life.
The choice of food is very important. Bees are an excellent example. A queen-bee which feeds on so-called royal jelly from its first days till the end of its life lives for two or three years. The worker bees receive this miraculous food for only the first two days of their lives and are given coarser food from the third day on. As a result they do not become completely fertile females and live onfy for two or three weeks.