CHAP, v.] NUTRITION. 839 



the body has not availed itself. The corrections thus necessary 

 for the faeces vary very considerably according to the nature of the 

 diet and to the personal powers and special circumstances of the 

 individual. In the case of animals, they will differ with different 

 kinds of animals ; in the case of a dog fed on a meat diet it has 

 been calculated that something less than 200 calories should be 

 deducted from the energy of each gramme of the meat. The 

 energy thus lost by the faeces in the case of man at least bears 

 under ordinary circumstances most on the proteids ; very little is so 

 lost by the fats and not a great deal by the carbohydrates. Then 

 again besides the urea we have to consider the other combustible sub- 

 stances in urine ; and still other smaller corrections, which we need 

 not consider here, have also to be made. Hence the actual avail- 

 able energy of the several food-stuffs falls short, in the case of 

 each food-stuff, of that indicated by the figures given above, and in 

 the case of the proteids falls considerably short. Since the cor- 

 rections to be made are as we have seen variable, any statement as 

 to the average amount of available energy can only be an approxi- 

 mate one, depending on the appreciation of the average amount of 

 correction necessary. Some authors reduce the available energy 

 of proteid (meat) to 4000 cal., and of fat to 9300 cal. per grm. 

 But this is probably too great a reduction, and we may perhaps 

 venture to make the data as follows, 



1 grm. proteid 4500 calories. 



1 grm. fat 9500 



1 grm. carbohydrate 4000 



The average diet of an average man, that is the average 

 amount of each food-stuff respectively taken daily, may be deter- 

 mined experimentally or statistically. Thus a man may deter- 

 mine by a series of trials the diet on which, while neither losing 

 nor gaining weight, maintaining 'nitrogenous equilibrium,' and 

 otherwise keeping the composition of his body fairly constant, 

 he enjoys good health. Or an average may be struck of a large 

 number of diets used by various people. We shall have something 

 to say of this latter statistical method when we come to speak of 

 diet. For the present purpose we may use one arrived at experi- 

 mentally which we will speak of as Ranke's diet, since it was 

 determined by a physiologist of that name from observations on 

 himself. It was composed of 100 grm. proteid, 100 grm. fat, 

 240 grm. carbohydrate. Such a diet would give 



100 grm. proteid (4500) 450,000 calories 



100 grm. fat (9500) 950,000 



240 grrn. carbohydrate (4000) 960,000 



2,360,000 



We may, in passing, call attention to the fact that the proteids 

 supply a relatively small part of the total energy, and that the 



