THE FATS 65 



cereals and grains, potatoes, and most vegetables are rich in 

 carbohydrates ; as are also sugar, molasses, honey, and maple 

 sirup. The foods of the first group are valuable because of 

 the starch they contain ; for example, corn starch, wheat 

 starch, potato starch. The substances of the second group 

 are valuable because of the sugar they contain ; sugar contains 

 the maximum amount of carbohydrate. In the sirups there 

 is a considerable quantity of sugar, while in some fruits it is 

 present in more or less dilute form. Sweet peaches, apples, 

 grapes, contain a moderate amount of sugar; watermelons, 

 pears, etc., contain less. 



Carbohydrates, whether of the starch group or the sugar 

 group, are composed chiefly of three elements : carbon, 

 hydrogen, and oxygen ; they are therefore combustible, and 

 are great energy producers. On the other hand, they are 

 worthless for cell growth and repair, and if we limited our 

 diet to carbohydrates, we should be like a man who had fuel 

 but no engine capable of using it. 



62. The Fats. The best-known fats are butter, lard, olive 

 oil, and the fats of meats, cheese, and chocolate. When we 

 test fats for fuel values by means of a calorimeter (Fig. 26), we 

 find that they yield twice as much heat as the carbohydrates, 

 but that they burn out more quickly. Dwellers in cold climates 

 must constantly eat large quantities of fatty foods if they are 

 to keep their bodies warm and survive the extreme cold. 

 Cod liver oil is an excellent food medicine, and if taken in 

 winter serves to warm the body and to protect it against the 

 rigors of cold weather. The average person avoids fatty 

 foods in summer, knowing from experience that rich foods 

 make him warm and uncomfortable. The harder we work and 

 the colder the weather, the more food of that kind do we re- 

 quire ; it is said that a lumberman doing heavy out-of-door work 

 in cold climates needs three times as much food as a city clerk. 



CL. GEN. SCI. 5 



