A STUDY OF THE MUSCLES 203 



solid ingredient. Mineral matter and fats are also present 

 in small quantities, even in the leanest of muscle. During 

 the period of growth all these nutrients should be sup- 

 plied for muscle building, but proteid is absolutely essen- 

 tial. Grape sugar is also found to be an important food 

 during muscular contraction. When training for contests 

 the diet of athletes is carefully regulated: rare meats, 

 coarse breads, eggs, vegetables, and fruits are supplied in 

 generous quantities ; pastry and fats are reduced to a mini- 

 mum. Tobacco ' and alcohol in any form, however, are 

 absolutely prohibited. Such a diet is undoubtedly far more 

 wholesome to develop a healthy boy or girl, man or woman, 

 than are the rich gravies, pastries, and condiments which 

 are found on too many tables. 



Fresh Air. Healthy muscle is absolutely powerless, how- 

 ever, unless in addition to food, it receives a supply of oxy- 

 gen; for all muscular energy is produced by oxidation. 

 Impure air, besides being deficient in oxygen, contains carbon 

 dioxid and other gases that are exceedingly harmful to the 

 tissues (see p. 221). Well-ventilated sleeping rooms are 

 most essential for healthy living, for during the night the 

 body gets rid of much of the waste carbon dioxid that is 

 formed during the day. 



Exercise. It seems like a contradiction to say that the 

 only way to get more and better muscle is to destroy what 

 we already have. Every one knows, however, that if the 

 muscles of the arm or the leg are not used for a time, they 

 become weak and flabby, and yet every time a muscle is 

 made to contract, some of its substance is oxidized. New 

 muscle must then be formed by the process of assimilation 

 to take its place. 



A certain amount of vigorous exercise each day is essen- 

 tial if one is to keep one's body in the best physical condi- 

 tion. This amount of course varies with the individual. It 

 should never be carried to an excess, resulting in exhaustion, 

 but should usually be at least the equivalent of a five-mile 



