460 FOOD [CH. XXVIII. 



15 to 18 grammes of nitrogen. These substances are derived from 

 the metabolism of the tissues, and various forms of energy, mechanical 

 motion and heat being the chief, are simultaneously liberated. During 

 muscular exercise the output of carbon greatly increases ; the increased 

 excretion of nitrogen is not nearly so marked. Taking, then, the 

 state of moderate exercise, it is necessary that the waste of the tissues 

 should be replaced by fresh material in the form of food ; and the 

 proportion of carbon to nitrogen should be the same as in the excre- 

 tions : 250 to 15, or 16'6 to 1. The proportion of carbon to nitrogen in 

 proteid is, however, 53 to 15, or 3*5 to 1. The extra supply of carbon 

 must come from non-nitrogenous food viz., fat and carbohydrate. 

 Moleschott gives the following daily diet : 



Proteid 120 grms. 



Fat 90 



Carbohydrate 333 



Kanke's diet closely resembles Moleschott's ; it is 



Proteid . 100 grms. 



Fat 100 



Carbohydrate 250 



Such typical diets as these must not be considered as more than 

 rough averages of what is necessary for a man in the course of the 

 day. Actual experience shows that in the diets of different nations 

 there are considerable variations from this standard without the 

 production of ill effects. Age, and the amount of work done, also 

 influence the amount of food necessary ; growing children, for instance, 

 require a relatively rich diet ; thus, milk, the diet of the infant, is 

 proportionally twice as rich in proteids, and half as rich again in 

 fats, as the normal diet given above. During work more food is 

 necessary than during inactivity. 



Some attention has recently been devoted to the question whether 

 as much daily food is necessary as given in the foregoing paragraphs. 

 Hirschfeld showed that for a short time nitrogenous equilibrium can 

 be maintained on a smaller daily supply of nitrogen than 15 grammes. 

 But experiments of others extended over a longer period have shown 

 that sooner or later the body begins to waste if the 15 grammes daily 

 are not supplied. This objection, however, cannot be urged against 

 the experiments of E. 0. Neumann, which lasted for three years. The 

 weak point of this research is that it was made only upon one person, 

 namely himself. His diet on the average consisted of 74 grammes of 

 proteid, 117 of fat, and 213 of carbohydrate (equivalent to a total heat 

 value of 2367 large calories, see Chapter XL.). He lost no weight, and 

 part of the time even gained weight ; he enjoyed good health, and did 

 his daily duties without inconvenience. A practical point is that his 

 food cost him only 7Jd. a day. 



