112 ELEMENTARY BIOLOGY 



down, but the manner of cooking may have an influence upon 

 the digestion. 



144. Cooking. There are three or four primary uses of cook- 

 ing that can be understood from a biological point of view : 



1. Cooking breaks up and softens the cell membranes, thus 

 liberating the proteins, fats, and carbohydrates. 1 



2. The chemical changes produced in meats, vegetables, 

 eggs, cereals, etc. by the action of heat result in the formation 

 of substances that are especially attractive to the sense of smell, 

 and thus react favorably on the secretion of digestive juices. 



3. The action of heat (with or without moisture) upon starch 

 results in breaking up the starch grains and in making them 

 more easily digested. 



4. Cooking has the further effect of destroying any germs 

 of bacteria or other microbes (see Chapter LXXI) that may be 

 present in the raw food, thus lessening the danger of trans- 

 mitting an infectious disease or a parasite (see p. 341), and 

 making it easier to preserve the food against decay. 



Another result of cooking that has only recently received the 

 attention it deserves is the wastefulness involved in certain kinds of 

 cooking. This is a matter that is not strictly biological, although it 

 should be considered in connection with the subject of feeding. One 

 particular kind of waste, however, has biological significance. That is 

 the waste of mineral matters brought about by the boiling of food 

 and then throwing away the water which contains the valuable food 

 salts. Of course, with more scientific cooking these wastes will be 

 avoided, and our food as served to us at the table will contain the 

 necessary minerals, as well as the proteins, fats, and carbohydrates. 



145. Food economy. Another important consideration in the 

 selection and preparation of food is the matter of cost. For 

 all practical purposes a few cents' worth of corn meal may 



1 To a certain extent the materials that make up the cell walls in meats 

 become digested and thus contribute to the total food supply. The cellulose 

 that makes up the cell walls of plant tissues cannot be digested in the human 

 body ; but it is digested into sugars by the juices of many animals, such as 

 cows and other grass-eaters. 



