FIG. 141.—Rachitic baby and normal baby of the same age, showing dwarfism and deformities caused by rickets. (By courtesy of Dr. Leonard Findlay, Glasgow, Scotland.) ] =Rickets.= The actual cause of rickets is not definitely known, but the disease apparently results from wrong proportions between calcium and phosphorus, and to unfavorable amounts of these two substances in the food. Accordingly, it may be said to be due to a faulty diet—one which is rich in carbohydrates and poor in fats and possibly some substance as yet unrecognized—and it may be both prevented and cured by what is now regarded as suitable feeding. The chief characteristics of the disease are arrested growth and softening of the bones, with dwarfism and deformities as a result. (Fig. 141.) It is essentially a disease of infancy, occurring as a rule, between the fourth and eighteenth months but some of its unfavorable effects, such as bone deformities and poor resistance to disease, may persist throughout life. Although babies rarely die of rickets alone, it is one of the most serious of all health problems and obstacles to normal development and stability, since it predisposes to such diseases as bronchitis, pneumonia, tuberculosis, measles, and whooping cough and in general greatly enfeebles the powers of resistance and recuperation. It is common among babies who are fed solely or continuously on heated milk, either boiled or canned, and on proprietary foods and sweetened condensed milk. There has been some speculation about the possible relation between rickets and fat-soluble A, but no definite conclusions have yet been reached. It is known, however, that rickets may develop among nursing babies whose mothers are on faulty diets, and that the disease may be prevented and cured by the administration of cod-liver oil, which is rich in fat-soluble A. Sunshine, also, seems to have a pronounced effect in preventing and in curing the disease. [Illustration: FIG. 142.—Exterior of thorax of normal rat and rachitic rat of same age. The latter shows dwarfism and deformities resembling pigeon breast so frequently seen in human beings suffering from rickets. (From The Newer Knowledge of Nutrition, by E. V. McCollum.) ]