Chap, v.] NUTRITION. 659 



egesta equal to that of the ingesta. To make sure that under 

 such a diet the body was remaining of the same composition 

 there ought to be evidence of a carbon equilibrium also, other- 

 wise during the period of the experiment fat might be being 

 replaced by water (see § 415); but this is unlikely, and we 

 may therefore accept the method as a fair one. It has given 

 in the hands of two different observers the following somewhat 

 different results, the diet A being that alread}^ quoted in § 421 : 



The total (available) potential energy is respectively 2310, and 

 3035 calories. 



On the whole the diets gained by the two methods agree 

 very largely. To put down a single column of figures as " the 

 normal diet " would be to affect a vain and delusive accuracy. 

 If we desire, for theoretical purposes, to select some one set of 

 figures rather than others, we might be influenced by the con- 

 siderations that the lower amount of proteids in the experi- 

 mental diet was nearer the mark than the higher amount of 

 some of the statistical diets, and further that, where cost is not 

 of moment, the substitution of fat for an excess of carbohydrates 

 is desirable. We should be thus led to take the experimental 

 diet A as on the whole the best or most ' normal ' one, and that 

 is the one which we employed in the calculations of § 421. It 

 will be observed that the potential energy of this diet is less 

 than that of any of the others, and, as we said while then speak- 

 ing of it, may be considered low ; but there was no evidence 

 that it was insufficient. Still it must be remembered that 

 neither it nor any of the others is to be regarded as distinctly 

 proved to be the real normal diet. Against the experimental 

 diet we may urge that the number of experiments have been 

 few and conducted on a few individuals onty at most, and that 

 a larger number of experiments, with a variety of combinations 

 of different amounts of the several food-stuffs, might lead to a 

 different result ; that for instance with certain amounts of fats 

 and carbohydrates, the amount of proteid needed to maintain 

 healthy bodily equilibrium, including nitrogenous equilibrium, 

 might be reduced much below the 100 grammes, especially if 

 particular kinds of proteids, fat or carbohydrates were used, 

 and especial attention (see § 420) were paid to the salts. 

 And indeed a considerable number of observations have been 

 made tending to shew that a man of average size and weight 



