CHAPTER VII. 



NUTRITION IN TERMS OF ENERGY. 



Measurements of meclaanical and chemical operations by units of 

 heat. Fuel value of food constituents and animal products. Heat 

 value of foods to the animal. — Relation of units of heat to units of 

 work. Energy consumed in operations of digestion. — Distinction 

 between fibrous and non-fibrous foods. Relation of heat valtie of 

 'food to heat value of animal increase obtained. 



Fuel Value of Foods and Animal Products. — The 



quantitative results both of mechanical and chemical 

 operations are often best expressed in terms of energy. 

 The most convenient form of energy to make use 

 of in such discussions is heat. The unit of heat 

 employed is the " calorie," w^hich represents the 

 quantity of heat required to raise one gram of v^ater 

 from 0^ to V on the scale of the Centigrade ther- 

 mometer. A Calorie one thousand times larger than 

 this is employed for the expression of large quantities 

 of heat, and this will be employed in the present 

 work.^ 



The relative quantities of energy supplied by the 

 different organic constituents of food, or stored up in 

 the various constituents and products of the animal 

 body, are shown by the quantities of heat produced 

 when these substances are completely burnt. These 

 quantities of heat express the " fuel value " of the 

 substance. When one gram of the following dry sub- 



* The large Calorie should always be spelt with a capital. 



