GOVERNMENTAL REGULATION OF FOODS 351 



students while writing a very difficult examination, and it was found 

 that no more energy was set free from the hody than when they were 

 simply writing nonsense. However, a very small part of the potential 

 energy of the food always takes the form of electrical energy and elec- 

 trical energy is manifested whenever nervous tissue (brain, nerve, etc.) 

 is active. It is possible then that the reason no extra heat energy was 

 given off from the body when the brain was working hard is because 

 this electrical energy simply took the place of other forms of energy 

 (like the secretory processes of glands, etc.), in which case it would 

 not be correct to say that brain work is not done at the expense of 

 potential energy. The subject requires much more study than has yet 

 been given to it. 



It will be evident from the discussion thus far that it is the energy 

 content of the food which a person is concerned primarily to know in 

 order to judge the economy of its use. Ordinarily if one takes care 

 merely to supply himself enough heat energy and takes care also to eat 

 a variety of food the other requirements will be automatically regulated 

 by the appetite. Failure properly to adjust the energy supply to the 

 actual requirements result in depletion which may subject one to disease, 

 or, on the other hand, may lead to obesity. 



But it would be a serious mistake to ignore the other chief purpose 

 of foods — namely, their value as tissue builders and restoratives. 

 While not more than one fifth of the dry weight of our foods find a 

 permanent lodgment in the body, it is obvious that the functional 

 activity of the tissues could not be kept up indefinitely without these 

 constituents of which tissues are formed. Still less could growth of the 

 body in early life be maintained. 



Among these constituents the most important is that class of sub- 

 stances known to physiologists as 'proteins, exemplified by the white of 

 egg, the casein of milk, the gluten of bread and par excellence the flesh 

 of animals. The actual requirement of the body for these substances 

 is much less than is ordinarily supposed. In starvation, when the body 

 is living at the expense of its own substance, about 13 per cent, of its 

 energy is derived from the breakdown of proteins or the nitrogenous 

 substances. The remaining 87 per cent, is derived from the body fat 

 and glycogen, which is the form in which the body stores up starches 

 and sugars. Theoretically the body would be kept in perfect equilibrium 

 then if the food contained 87 per cent, of the total energy in the form 

 of carbohydrates and fats and 13 per cent, in the form of protein. In 

 fact, many persons have found that they keep in better physical condi- 

 tion if they take somewhat less than 13 per cent, in the form of protein, 

 for with a generous suply of carbohydrate in the food the waste of 

 proteins from the body is considerably less than in starvation. The 

 dietaries suggested above for various sorts of workers, however, have 



