ENERGY IN FEEDINGSTVFFS AND ITS USES 97 



excreted by an animal can be measured. It consists of a 

 closed chamber large enough to accommodate the animal 

 under experimentation. Fresh air is pumped into the 

 chamber and the vitiated air is pumped out and analyzed 

 to determine the gases excreted by the animal. The feces 

 are collected by means of a digestion harness, and the urine 

 by means of a rubber funnel and duct strapped on to the 

 belly of the animal. The heat given off by the animal is 

 determined by the rise in temperature of a known amount 

 of water which flows through radiators in the chamber and 

 absorbs the heat given ofT by the animal. The only res- 

 piration calorimeter in this country large enough for exper- 

 iments with cattle is that used by Armsby at the Institute 

 of Animal Nutrition of the Pennsylvania State College.^ 

 Figure 22 shows this respiration calorimeter. 



In determining the metabolizable energy of a feedingstuff, 

 its gross energy is determined by the bomb calorimeter. 

 A known amount of it is fed to an animal wearing a digestion 

 harness and urine funnel in the respiration calorimeter. The 

 feces, urine, and combustible gases are collected, and the 

 energy lost through them is determined by means of the 

 bomb calorimeter. The energy of the urine, feces, and 

 gases subtracted from the gross energy of the feedingstuff 

 gives the amount of the metaboHzable energy in the feeding- 

 stuff. 



Uses of the Metabolizable Energy. — The metaboHzable 

 energy of the ration serves for three general purposes in the 

 animal body: (1) it suppHes energy for carrying on the 

 different forms of work of the animal body ; (2) in certain 



1 For a detailed description of this respiration calorimeter, see Penn. 

 Exp. Sta. Bui. 104. 



