FEED STUFFS AS A SOURCE OF ENERGY 63 



"Second, as already pointed out, the animal body has to ex- 

 tract its real fuel material from' its feed, separating it from the 

 relatively large proportion of useless material which it excretes. 

 To efife;ct this separation requires work and consumes energy, 

 and this energy, of course is not available for other purposes. 

 Moreover, when the animal eats more feed than is required sim- 

 ply to furnish energy to run its machinery and hence is able to 

 produce meat or milk, the process of converting the food into 

 suitable forms to store up in the body seems to require a further 

 expenditure of energy. 



"Total Chemical Energy not Always an Indication. — It is not, 

 then, the total chemical energy contained in a feeding stuff 

 which measures its value as fuel material to the body, but what re- 

 mains after deducting the losses in the unburned materials of the 

 excreta and the energy expended in extracting the real fuel mate- 

 rials from the feed and transforming them into substances which 

 the body can use or store up. For example, while 100 pounds 

 of corn meal contain, as stated, about 170.9 therms of chemical 

 energy, only about 88.8 therms remain, after all these deductions 

 have been made, to represent the actual value of the corn meal 

 as a source of energy to the organism." 



Respiration Calorimeter or Respiration Apparatus. — ^The chemi- 

 cal energy of a feed stuff is easy to determine but in order to 

 find out the amount utilized or the production value, the respira- 

 tion calorimeter or respiration apparatus is used which is an air- 

 tight chamber in which man or animal is kept and food and air 

 introduced. To determine the production value or the energy 

 utilized, accurate data must be kept on the income and outgo of 

 all materials. The income includes the food, composition and 

 amount fed. The outgo includes feces, urine, perspiration, com- 

 bustible gases, storage of tissue, heat and work. One must rea- 

 lize that an apparatus capable of measuring all these things (solids 

 and gases) is complicated and expensive. To secure the energy val- 

 ues of feeds require considerable work and the expenditure of 

 much time. 



The respiration apparatus may be used for man as well as 

 for animals. 



