736 MAN'S PHYSICAL WELFARE Proteins contain nitrogen and sometimes sulfur and phosphorus in addition to carbon, hydrogen, and oxygen. They consist of long chains of different amino acids, twenty of which are formed in the digestion of proteins. Some proteins, the complete proteins, contain all the amino acids required to build and repair the tissues of the body, while other proteins contain only a portion of the amino acids required by the body. Large muscles are not obtained by eating an excess of proteins. The protein matter not utilized by the body is broken down, part of it being stored as fat, while the nitrogen portion is excreted in the urine. Excessive quantities of proteins should be avoided inasmuch as they place too heavy a tax on the excretory organs involved. The quantities of carbohydrates, fats, and proteins are measured in terms of calories. (See Unit IV, Section 3.) About 70-90 grams, or about 10 per cent of the total food calories, is considered to be the optimum quantity of protein in the daily diet. Growing children require more protein in their diet than do adults. In general, the average American diet is overinsured in regard to proteins. Vitamins are important organic compounds which occur in our foods and act as physiological catalysts. They will be discussed in the next Section. The minerals in our foods are calcium, phosphorus, iron, iodine, potassium, sulfur, sodium, chlorine, and magnesium. These minerals are usually present in adequate amounts in our diet with the exception of the first four. Definite provision should be made for these four minerals. Calcium and phosphorus are extremely important because they build the bones and teeth. Calcium influences the clotting of blood and helps to maintain the normal action of the nervous system. Calcium is the mineral required in the largest quantities by the human body, and it is calcium that is most often present in inadequate amounts in the American dietary. Iron is essential for the building of the hemoglobin of the red blood corpuscles. Iodine, although required in only very small amounts, is necessary for the proper functioning of the thyroid gland. Vegetables grown in regions where the soil is low in iodine contain very little iodine, whereas vegetables grown in regions where iodine is more abundant wnll not be deficient in iodine. In the regions where there is too little iodine in the soil, goiters are common. Recent studies indicate that traces of manganese, zinc, arsenic, and cobalt are essential to the body, although there are only a few cases where deficiencies have caused trouble. Five per cent of our food is mineral matter. Excess mineral matter cannot be stored up, and the body excretes mineral matter every day
FOODS 737 regardless of whether the diet is deficient or overinsured in minerals. Under average conditions a man excretes from twenty to thirty grams of minerals per day. The Frequent Lack of Minerals in the American Dietary Is the Result of Modem Food Habits. Some foods are naturally richer in minerals than are other foods. Natural foods are often robbed of their minerals by refining processes such as the bolting of wheat, the polishing of rice, the refining of sugar in factories, or the peeling, and boiling of foods in water in the home. Some people are allergic to such foods as milk, eggs, or meat, which are good sources of certain minerals, while other people have established appetites for foods which are deficient in minerals. STUDY QUESTIONS 1. What is the Tyndall effect? Give a number of common examples. 2. What is the outstanding property of colloids? Explain why colloids exhibit this property. Give an application of this property. 3. Why do colloidal particles remain in suspension? 4. Why is the study of colloids important? 5. What is the source of the electrical charge on colloidal particles? 6. Explain the formation of deltas. 7. Why do colloidal particles show so much adsorption? 8. Compare the size of colloidal particles with that of molecules. 9. List the different types of colloids with two examples of each. 10. What are the two general methods for the preparation of colloids? 11. Give the principle of the Cottrell smoke-precipitation process. 12. Mention three practical applications of adsorption. 13. Differentiate between adsorption and absorption. 14. Present evidence that plants require certain minerals for proper growth. 15. What minerals are required by plants? Which of these minerals are frequently deficient in the soil and why? What are the sources of minerals in fertilizers? 16. What is meant by "hydroponics"? 17. What processes liberate minerals in the soil? 18. Why is chemical analysis of the soil important in agriculture? 19. How can one determine what fertilizer and how much of it is required for a given soil? 20. Do plant products always contain the same amounts of minerals? Why or why not? 21. List the foods required by animals and state the function of each. 22. What are the main dietary problems of the American people? 23. Which minerals are frequently deficient in the American dietary, and why are they deficient? 24. Why may it be said that "A man can be what he chews to be"? 25. Explain what happens to the excess quantities of each of the types of food constituents when they are contained in the dietary.