22 HUMAN PHYSIOLOGY 



four or four and a half of the energy-producing 

 foods. We thus consume a far greater amount of 

 starchy food and sugar than of albumen, casein, or 

 any of the other foods which repair the tissues. In 

 the case of hard work the proportions of both have 

 to be slightly increased, but still the working foods 

 must naturally assume a predominance. Nature 

 teaches us much the same lesson when we inves- 

 tigate the composition of the foods which she 

 especially employs for the nourishment and building 

 of the young animal. The composition of milk 

 shows us a perfect combination of the two classes of 

 foods for the purpose of body-building and for 

 energy-production. Milk contains not merely casein 

 or curd for the formation of tissue, but likewise sup- 

 plies fat and sugar of milk, which represent energy- 

 producing substances, in addition to water and 

 minerals. The case of the egg is similar. Out of a 

 few teaspoonfuls of yolk and white the body of the 

 bird is built up, this body exhibiting a complexity of 

 structure not far behind that of our own frames. 

 In the egg we find albumen, fat, water, and minerals ; 

 the combination necessary for the building of the 

 body being essentially that which in after-life is also 

 required for the body's support. 



FOOD-TAKING IN PRACTICE. We have seen that 

 most of the articles of diet we consume, with the 

 exception of such foods as water and minerals, 

 contain both classes of substances in varying pro- 

 portions. The experience of mankind, apart from 

 scientific teaching, has led him to the practice of 

 taking foods in such combination and in such 

 proportions as usually on the whole best conduce 

 to the nourishment of the body. In such combina- 

 tion of foods we receive the due proportions of the 



