52 HUMAN BIOLOGY 



into this essential ingredient of protoplasm. Hence, an 

 animal soon dies if it is not supplied with proteins. 



If a machine is to do a large amount of work, it must be 

 large enough and strong enough, and must have plenty of 

 fuel. This is true of the body machine. A man who does 

 hard work, and a good deal of it^ needs plenty of proteins 

 in his food to build up his tissues and keep them in repair, 

 and plenty of fats and carbohydrates for fuel. 



57. Uses of mineral matters and water. — The mineral 

 matters like phosphate and carbonate of calcium and magne- 

 sium are necessary for making bones and teeth, and for the 

 making of protoplasm (P. B., 43). Salt is used in large 

 quantities by all civilized nations; it makes food more 

 palatable and it is important in the making of digestive 

 fluids. 



Water is an essential constituent of protoplasm, and hence 

 the body needs it constantly. Water also aids iu dissolving 

 foods. A considerable amount is supplied by the water 

 contained in some of our solid foods, and we get the rest 

 from the water and other beverages that we drink. 



V. Cooking of Foods 



58. Importance of proper cooking. — Some of our foods, like 

 milk, nuts, and fruits, are eaten without being cooked. The great 

 majority, however, before they are taken into our bodies are changed 

 considerably. It is important for us to learn the essential prin- 

 ciples of good cooking, since food, as often prepared, loses much of 

 its flavor, becomes more or less indigestible, and is deprived of a 

 considerable percentage of its nutrition. 



59. Reasons for cooking animal foods. — In civilized com- 

 munities meats and other animal foods are usually cooked by broil- 

 ing, roasting, boiUng, or frying. The reasons for cooking the flesh 



