HEAT VALUE OF FOOD TO ANIMAL 121 



such a purpose, 100 of the digestible matter of starch, 

 100 of the digestible matter of oat straw of good 

 quality, 103 of meadow hay, 113 of wheat straw, 80 of 

 wheat gluten, and 43 of earthnut oil (all in the state 

 of digested substance) are equivalent quantities, and 

 produce a similar amount of heat when given to oxen. 

 The fat has thus 2'3 times, and the albuminoid 

 (wheat gluten) about 1*25 times, the value of starch, 

 while the digestible part of foods rich in cellulose, as 

 hay and oat straw, has a value similar to that of starch, 

 a somewhat lower value being, however, observed in 

 the case of wheat straw. 



The work, internal and external, done by an animal 

 can also be expressed in terms of heat. One Calorie 

 is equivalent to 425 meterkilograms ; that is to say, 

 the energy required to heat 1 kilogram of water one 

 degree would also raise 1 kilogram to the height of 

 425 meters. We shall discuss later on (pp. 176, 183) 

 the relations of food to mechanical work, we need here 

 only notice the work performed during the processes 

 of digestion, and during the production of new animal 

 substance. 



Energy used in Digestion.— Zuntz has determined 

 the amount of energy employed by the horse during 

 the mastication and digestion of various foods. He 

 has done this by determining how much more oxygen 

 is consumed during mastication and digestion than 

 before or after these operations are accomplished. The 

 energy involved in these operations is partly consumed 

 in mechanical and partly in chemical work. Zuntz 

 has expressed his results both in Calories and in terms 

 of the digested food reckoned as starch ; we shall give 



