290 ELEMENTS OF AGRICULTURE 



an apparatus known as the respiration calorimeter. There 

 are only three such instruments in the world, and this 

 is the only one used for experiments on domestic animals. 

 The apparatus is so constructed as to enable the operator 

 to keep an exact debit and credit account with the animal. 

 He determines the weight, chemical composition and 

 energy content of the feed given. He then determines 

 the amount of matter and of energy carried off in the 

 visible waste products, and in the gases carried off by 

 the lungs and skin and by fermentation in the digestive 

 tract. Finally, the apparatus is a calorimeter, i. e., a 

 heat measurer, by means of which the amount of heat 

 given off by the animal is determined. Having thus ob- 

 tained a complete record of the income and outgo from 

 the body, it is easy to compute whether the animal has 

 stored up any of the matter and energy of the feed, or 

 whether he has been living in part on his own tissues. 



In this manner, Armsby found that the following 

 amounts of the energy of the food were set free in the 

 animal, or were digested: 



Timothy hay 44 per cent 



Corn meal 77 per cent 



These figures represent the percentage of digestibility 

 of these particular samples of feed with the particular 

 animal used. With different lots of feed or a different 

 animal, they might be different. 



A part of this material is lost in digestion, so that it is 

 not all available for maintenance. The percentages of the 

 digested materials available for maintenance were: 



Timothy hay 63 per cent 



Corn meal : 78 per cent 



