CHAP, v.] NUTRITION. 633 



Meat, free from fat, 5103, and 5324. Fibrin 5511. Egg- 

 iillmmin 5579. Thus, taking round numbers we may say that 

 1 grm. of proteid material contains 5000 or 5500 calories of 

 potential energy, according as we use the lower or higher 

 determinations. 



Fat of beef or mutton 9069, 9365, 9423. Butter 7267 or 

 9192. Again in round numbers we may say that 1 grm. of fat 

 contains about 9000 calories. 



Arrowroot (nearly pure starch) 3912. Starch 4123. Cel- 

 lulose 4146. Dextrose 3692. Cane Sugar 3866. Here again, 

 taking round numbers, we shall not be far wrong in saying 

 that the potential energy of 1 grm. of carbohydrate material is 

 about 4000 calories. 



The combustion of 1 grm. of urea sets free an amount of 

 energy which has been determined by one observer at 2206, by 

 another as 2465 calories. We have seen ( 401) that 1 grm. 

 of proteid gives rise in the body to ^ grm. urea. Hence, to 

 obtain the energy of 1 grm. proteid material available for the 

 economy, we must deduct from its total potential energy, one 

 third the potential energy of 1 grm. urea, that is, in round 

 numbers 700 or 800 calories. This will give us 5000 700, or 

 5500 800, that is 4300 or 4700 calories, according as we take 

 the lower or higher data ; or we may take as a mean 4500 

 calories. The data then so far are as follows, 



1 grm. proteid 4500 calories. 



1 grin, fat 9000 



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 

 determined experimentally or statistically. Thus a man may 

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

 losing nor gaining weight and maintaining ' nitrogenous equi- 

 librium,' 416, he enjoys good health. Or an average may be 

 struck of a large number of diets used by various people. \\ V 

 shall have something to say of this latter statistical method 

 when we come to speak of diet. For the present purpose \\v 

 may use one arrived at experimentally which we will speak 

 of as Runke'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 gnu. carbohydrate. 

 Such a diet would give 



100 grm. proteid (4500) 450,000 calories. 



100 grm. fat (9000) 900,000 



240 grm. carbohydrate (4000) 960,000 



2,310,000 



