Uses of the Fats Energy 157 



fattening food, a feeding stuff nearly seven -tenths of 

 which consists of starch and its allies. Recent experi- 

 ments with milch cows leave scarcely any doubt that 

 milk fat may also be derived from carbohydrates. 

 These more recent views tend to magnify the impor- 

 tance of the carbohydrates as nutrients. 



FUNCTIONS OF THE FATS AND OILS 



So far as is at present known, the possible uses of 

 the food fats and oils and of the carbohydrates are sim- 

 ilar. In other words, both may serve as fuel and both 

 may be a source of animal fat. The differences are that 

 the supply of carbohydrates is much the larger, and 

 the fuel value of a unit weight of fats much the greater. 

 Moreover, it seems possible for a vegetable fat to be- 

 come deposited in the animal without essential change, 

 whereas fat formation from carbohydrates involves 

 complex chemical transformations. 



FOOD AS A SOURCE OF ENERGY 



The living animal, either as a whole or in some of 

 its parts, is constantly in motion. This means that 

 the animal mechanism is ceaselessly performing work. 

 Even if the body is apparently quiet, the heart beats, 

 pumping blood to all parts of the body, the lungs are 

 expanded and contracted, and the stomach and intes- 

 tines keep up the movements which are essential to 

 digestion. Besides, a living body is the seat of con- 

 tinuous, invisible and complex chemical and physical 

 changes that, if not work in the common meaning of 



