PHYSIOLOGICAL CHEMISTEY 



361 



Having determined how much energy will be required, we must now 

 find out how much food must be supplied to yield it. We can deter- 

 mine the caloric value of the various food-stuffs by burning them in a 

 chemical calorimeter. Since the end products of the combustion of 

 fats and carbohydrates (viz., C0 2 and H 2 0) are the same in the body 

 as in vitro, their physical caloric values for 1 grm. of the dry substances 

 are the same as their physiological, viz., 4'1 for carbohydrates and 9 3 

 for fats. A very important end product of the metabolism of protein 

 is, however, urea, which still contains some potential energy, so that 

 it has a physical heat value of its own. In order to find the physio- 

 logical heat value of protein, therefore, we must deduct from its physical 

 value the physical value of the amount of urea arising from it. By 

 this means it has been shown that the physiological heat value of 

 protein is practically the same as that of carbohydrate, viz. 41. 



By an examination of the diets taken by various classes of people, 

 averages of the relative amounts of the various classes of food-stuffs 

 have been obtained. Such a table for a man doing an ordinary amount 

 of work is the following : 



Protein, 125 grammes. 1 



Carbohydrate, 500 grammes. 



Fat, 50 grammes. 



This diet yields : 



Such a diet is represented approximately by : J Ib. prime lean meat; 

 1J Ibs. bread; 2 oz. butter; \ pint milk; 1 Ib. potatoes; and J Ib. 

 oatmeal. 



Demonstration. The quantities of foods given above have been 



The small calorie is written with a small "c," the large one with a capital "C." 

 The heat unit can be transformed into units of work by multiplying by 425 '5, a unit 

 of work being expressed as the amount of force necessary to raise a weight of one 

 gramme to a height of one metre a gramme metre or of one kilogramme to the 

 same height, a kilogramme metre. 

 1 Dryweight. 



