xi] MILK AS A FOOD 167 



necessary fuel to keep the animal machine working, 

 this is more especially the function of the other two 

 groups of nutrients, viz. the fat and the carbohydrates. 

 But since the carbohydrates are unable to discharge 

 any functions as flesh-formers, and can form fat 

 probably to only a very limited extent, their charac- 

 teristic function may be described as heat-givers. 



And here it may be well to point out with regard 

 to the value of the three members of the three groups 

 of nutrients as heat-givers, that they are not all 

 equal in this respect, and that fats, when burned in 

 the body, yield 2J times as much heat as an equal 

 weight of a protein or carbohydrate nutrient. A 

 common method of comparing different foods is to 

 compare their heat-giving value. Another method 

 of comparing foods is by calculating what has 

 been named their albuminoid or nutritive ratio, 

 viz. the ratio which their flesh-forming nutrients 

 bear to their heat-giving nutrients. The amount of 

 albuminoids or flesh-forming nutrients in almost all 

 foods is very much less than the amount of fat and 

 carbohydrates. It is customary, therefore, in cal- 

 culating the nutritive ratio, to take the amount of 

 albuminoids as 1. To obtain the other number of 

 the ratio, the amount of fat present in the food is 

 first multiplied by 2J, and then added to the weight 

 of the carbohydrates. Thus, supposing that a food 

 contains per pound, 2 ounces of albuminoids, 2 



