72 FOOD 



of animal origin, but some protein material is also found in the 

 vegetable world ; peas and beans have an abundant supply of 

 this substance, and nuts are likewise rich in it. This class of 

 foods contains carbon, oxygen, and hydrogen, and in addition 

 two substances not found in carbohydrates or fats namely, 

 sulphur and nitrogen. The living cells of the body always 

 contain nitrogen, and old cells cannot be repaired, and addi- 

 tional cells cannot be formed, unless nitrogen is supplied to 

 them. Proteins always contain nitrogen, and hence they are 

 frequently spoken of as the nitrogenous foods. Since proteins 

 contain all the elements found in the two other classes of foods, 

 they are able to contribute, if necessary, to the store of bodily 

 energy; but their main function is up-building, and the diet 

 should be chosen so that the protein does not have a double 

 task. It has been estimated that 300,0x30,00x3 blood cells alone 

 need daily repair or renewal. When we consider that the blood 

 is but one part of the body, and that all organs and fluids have 

 corresponding requirements, we realize how vast is the work to 

 be done by the protein. For an average man four ounces of dry 

 protein matter daily suffice to keep the cells in normal condition. 

 Mineral matter. Mineral matter, such as iron, phosphate, 

 calcium, and magnesium, is needed by the body for teeth, 

 bones, and nails, and for cells in general. Iron is used by the 

 blood cells which carry oxygen; calcium and phosphorus are 

 used in the building up of bones ; and phosphorus and sodium 

 occur in every cell and are necessary to cell growth and 

 activity. Mineral matter is an essential part of the diet. 

 Usually mineral matter is found in greatest abundance in plant 

 food of low fuel value, such as lettuce, water cress, spinach, 

 cucumbers, cabbage, and tomatoes. Animal foods contain very 

 little mineral matter, and hence a mixed diet of plant and 

 animal foods is best. The following table shows the value of 

 plant foods in supplying the body with mineral matter. 



