NUTRITION AND THE CHANGES IN THE TISSUES. 371 



of this carbon, hydrogen and oxygen will be proportional to 

 the amount of work done. This at once explains, too, 

 the increased breathing of oxygen with increased exertion, 

 and also explains the necessity for increased amounts of food 

 with increased exertion. 



But such an increase of foods need not at all be proteid, 

 but may be fatty or carbohydrate. Of course a certain 

 amount of proteid is absolutely indispensable, since proteid 

 alone can replace the slight wear and tear just referred to. 

 To eat more proteid food than necessary to replace this loss 

 simply necessitates the body to eliminate it. In physiolog- 

 ical terms we speak of a person or animal as being in a pro- 

 teid equilibrium when the nitrogen taken in his foods equals 

 in amount the nitrogen eliminated from the kidneys. In 

 the same way we speak of a person as being in a carbon 

 equilibrium when the carbon taken in his foods is equal to 

 the carbon eliminated from his lungs. If more is eliminated 

 than is taken in in any of these cases starvation and emacia- 

 tion are the result. If more of these foods is taken than is 

 needed one or both of two results may follow: Some of 

 the surplus food, as for instance the fat, may be stored in 

 the tissues for future use and so the person become fat, in 

 the ordinary use of that term; or secondly, the nutritive 

 equilibrium of that individual raised to a higher level. This 

 needs a word of explanation. It is possible in a long con- 

 tinued diet to establish a nutritive equilibrium at an almost 

 starvation diet. The tissues of the body will adjust them- 

 selves to the income, and finally establish an equilibrium at 

 that level. This means that the losses will exactly balance 

 the gains and the body will seem to hold its own. If, now, 

 the amount and quality of the foods be suddenly increased, 

 there is at first a tendency of the body to eliminate these 

 extra foods, especially the proteids, but finally the tissues 

 will adjust themselves to the new order of things, will use 

 up increased quantities of food in their daily work, until 

 finally a new nutritive equilibrium is established. As a sim- 

 ple analogy an illustration may be taken from the social 



