120 THE HUMAN BODY. 



heat, makes it a good food in cold weather for persons with 

 a good digestion. Pigs are especially liable to a parasite, 

 called trichina, which lives in their muscles, and may be 

 transferred thence to man, sometimes causing death. Hence 

 pork should always be thoroughly cooked. Salted meats of 

 all kinds are less digestible and less nutritious than fresli. 

 Milk contains an albuminous substance (casein), also fats 

 (butter), and a sugar, known as sugar of milk, in addition 

 to useful mineral alimentary principles. It will support life 

 longer than any other single food. Cheese consists essen- 

 tially of the casein of milk: it is a very nutritive albuminous 

 food. Eggs contain albumens and fats, and have a high 

 nutritive value: they are more easily digested when cooked 

 soft than hard. Wheat contains more than a tenth of its 

 weight of proteids, more than half its weight of starch, 

 some sugar, and a little fat. The proteid of wheat flour is 

 mainly gluten, which when moistened with water forms a 

 tenacious mass, and this it is to which wheaten bread owes 

 its superiority. When the dough is made, yeast is added 

 to it and causes fermentation by which, among other 

 things, carbon dioxide gas is produced. This gas, im- 

 prisoned in the tenacious dough and expanded by heat dur- 

 ing baking, forms cavities in it, and causes the dough to 

 "rise" and make "light bread," which is not only more 

 pleasant to eat but more easily digested than heavy. Sonic 1 

 grains contain a larger percentage of starch, but none have 

 so much gluten as wheat; when bread is made from them 



Why should pork be well cooked? How do salted meats differ in 

 value as articles of diet from fresh? What foodstuffs exist in milk? 

 What one food will support life longest? What is the chief aliment- 

 ary principle in cheese? What is the nutritive value of cheese? What 

 makes the value of eggs as foods? Are they more easilv digested soft 

 or hard boiled? What foodstuffs exist in wheat? Why is wheaten 

 bread lighter than that made from other grains? 



