514 NUTRITION. 



health, neither gained nor lost in weight, and remained, moreover, in nitro- 

 genous equilibrium with the nitrogen of the 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 replaced by water 

 (see 435; ; 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 already quoted 

 in 441 : 



A B 



Proteids 100 grammes 118 



Fats 100 " 56 



Carbohydrates 240 " 500 



Salts 25 



Water 2600 



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 considerations that the lower amount of proteids in the experimental 

 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 441. 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 speaking of it, may be considered low ; 

 but there was no evidence that it was insufficient. Still it must be remem- 

 bered 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 only 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 be- 

 low the 100 grammes, especially if particular kinds of proteids, fat, or carbo- 

 hydrates were used, and especial attention (see 440) were paid to the salts. 

 And, indeed, a considerable number of observations have been made tending 

 to show that a man of average size and weight may continue in nitrogenous 

 equilibrium and in good health with a daily ration of much less than 100 

 grammes proteid, with as little as 40 grammes for example. To this we 

 shall have to refer in speaking of a vegetable diet. Against the statistical 

 diet, on the other hand, we may urge that instinct is not an unerring guide, 

 and that the choice of a diet is determined by many other circumstances 

 than the physiological value of the food. 



464. Taking, however, some such diet as the above to be the approxi- 

 mately true normal diet, we may call attention to the fact that the normal 

 diet is made up of each of the three great food-stuffs, carbohydrates being in 

 excess. W 7 e may here remark incidentally that the diets of both the car- 

 nivora and herbivora agree with that of omnivora in containing all three 

 food-stuffs ; they differ from each other as to the relative proportions only. 

 As we have seen, the body may be maintained in equilibrium on proteid food 



