Relative Energij and Production Values 171 



cal uses and relative values of even the most promi- 

 nent individual compounds, we would be able to make 

 somewhat definite comparisons of the different feeding 

 stuffs. It must be confessed that information of this 

 specific kind is not as complete as one could wish. 

 Its acquirement is very difficult and its present status 

 is in some particulars unsatisfactory. Investigations 

 so far conducted are not only insufficient to final con- 

 clusions, but researches by different observers have re- 

 sulted in a conflict of opinion in some cases. 



RELATIVE ENERGY AND PRODUCTION VALUES OF THE 

 NUTRIENTS SINGLY AND AS CLASSES 



It is satisfactorily established, as we have seen, 

 that protein, carbohydrates and fats have certain func- 

 tions in common, that is, that all three classes are 

 utilized as fuel, and that both carbohydrates and fats, 

 and perhaps protein, may be a source of body fat. 

 The question naturally arises. What is the relative 

 value of these unlike nutrients as a source of energy 

 and as fat-formers? Moreover, as each class is made 

 up of a variety of substances, unlike in physical and 

 chemical characteristics, can we consider the individual 

 compounds within the same class as nutritively equal ? 



Relative energy values.— As a source of energy, the 

 carbohydrates and their allies are properly regarded as 

 of first . importance because of their large relative use 

 as a fuel supply. These bodies, so far as they are 

 digestible, have been considered in formulating rations 

 as of practically equal value. It is well known that 



