Page:First course in biology (IA firstcourseinbio00bailrich).pdf/580

 Milk of cows is improperly called a perfect food by some writers. Although it contains the four classes of food stuffs, the proteid is in excess, the fuel food being deficient. Buttermilk is more digestible than sweet milk. Buttermilk and sugar form a valuable food for infants. Skimmed milk still contains the proteid, the most nutritious part of the milk. Sour milk, or "clabber," and curds pressed into "cottage cheese" are more digestible than sweet milk. Cream is more easily digested than butter, which is a solid fat. Cheese is a very concentrated proteid food, and should be eaten sparingly. Eggs are a valuable food. Is there more proteid or fat in eggs? (See Table.) Pork and veal are the most indigestible of meats. Fish is nearly as nutritious as meat. There used to be a supposition that fish nourished the brain because it contains phosphates; but there are more phosphates in meat than in fish, and more in grains than in meat.

Grains contain considerable proteid (gluten), but they especially abound in starch. Wheat flour contains more gluten than corn meal, hence it is more sticky, and retains the bubbles of gas so that the dough rises well in bread making. Eggs are sometimes added to corn meal to make it sticky and cause it to rise well. Which grain has the largest percentage of oil? (See Table.) Of starch? Of gluten? Which is poorest in gluten? Grains may be made to resemble fruit by long cooking at a high temperature (300° Fahr.), for their starch is thus changed to dextrin, a substance resembling sugar. You learned that the starch of fruit is turned into sugar as the sun ripens it. Dextrin is yellow and gives the dark color to toasted bread. It is changed to sugar almost instantly when brought in contact with saliva. It is used as a paste on postage stamps.

Vegetables contain much water and woody fiber. White potatoes are underground stems and are one fifth starch. Yams, or sweet potatoes, resemble roots, and contain both starch and sugar. Beans and peas are very nutritious. They have been called "the lean meat of the vegetable kingdom." They require boiling for several hours. If the skins are removed by pressing them through a colander, they are very easy of digestion. This purée of beans makes delicious soup. "Hull-*less beans" and "split peas" are also sold by grocers.

—1. Clothing and shelter for man or beast economize what kind of food? 2. Why should bread remain longer in the mouth than meat? 3. In snowballing, what is the appearance of the hands when they itch from cold? Extreme cold irritates and congests the stomach more quickly than it does the hands. Why is it that ice water does not satisfy the thirst, but often produces a craving to drink more water? 4. Should biscuits having a yellow