802 THE POTENTIAL ENERGY OF FOOD. [BOOK n. 



The total combustion of the following substances has given for 

 one gramme of each substance the following results expressed in 

 calories, that is in gramme -degree units of heat. 



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

 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. Cellulose 

 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 ( 507) 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 grm. 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 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 and maintaining ' nitrogenous equilibrium ', 

 522, 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 experimentally 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 (9000) 900,000 



240 grm. carbohydrate (4000) 960,000 



2,310,000 



