498 APPLIED BIOLOGY 



grams of protein for an average 150-pound man. Most 

 well-to-do people eat on the average more than 100 grams of 

 protein in meat daily, and also they get much additional 

 protein in milk, eggs, bread, all vegetables in fact, there 

 is some in most common foods.* 



While the amount of protein foods needed daily is quite 

 constant for the ordinary adult, the amount of the other 

 foods should vary with the amount of energy required. A 

 student certainly needs less fats and carbohydrates than a 

 laborer does. So long as digestion is good, variation in 

 weight is a good index to the amount of such foods needed ; 

 for if taken in excess and digested, there will likely be in- 

 creased weight due to food storage in the fat tissues of the 

 body. Loss in weight by an adult who daily eats as much 

 as 100 grams of protein indicates a need of more fats and 

 carbohydrates ; and whether starch, sugar, or fats should 

 be used depends upon availability, digestibility, and taste 

 of the individual. 



Growing animals and children require a higher proportion 

 of protein (see 422) than do adults, who alone have been 

 considered in the above discussion. 



421. Foods for Heat. As previously stated, birds and 

 mammals must maintain a constant body temperature. 

 To a large extent they do this by preventing excessive loss 

 from the skin (447). The production of heat is chiefly 

 the result of muscular activity. We all know how easily 

 we can keep warm by exercise on a cold day, but how un- 

 comfortably cold we often feel if we simply eat our regular 

 meals and keep quiet. For this reason we require more 

 clothing or covering when sleeping, for then only the circu- 

 latory and respiratory muscles and chemical changes in the 

 digestive organs are the chief sources of heat production. 



* Per cent of protein in foods : lean meat 15-22 ; eggs 15 ; white bread 

 9 ; dried beans 22 ; potatoes 2 ; peanuts 25 ; butter 1 ; outmeal 16 ; olive 

 oil ; sugar ; milk 3 ; green corn 3 ; fish 15-20 ; apples 0.4 ; rice 8. 



