46 PRINCIPLES OF FEEDING FARM ANIMALS 
The figures given in the table show the amounts of chemical 
energy (in therm units) which are set free when 100 pounds of 
different pure nutrients and common feeding stuffs are completely 
burned. We note that the figures range for protein from 256 to 
272 therms, for carbohydrates from 170 to 190, and for fats from 
421 to 427, while those for feeding stuffs vary from 170 (rice 
meal) to 267% (flaxseed meal). Fats yield about 2.25 times as much 
energy on combustion as starch, and this factor has been commonly 
.__ Fig. 9.—A view of the respiration calorimeter at the Pennsylvania Experiment Sta- 
ie ae calorimeter chamber in which the animal on the experiment is kept, to the left. 
rmsby. 
adopted for the heat-producing value of fats as compared with that 
of starch and of carbohydrates in general. 
The figures given represent the total potential energy that is 
locked up in the materials, but they do not show the energy that is 
available to animals fed the different feeding stuffs or nutrients. 
The reason for this is three-fold: 
First, feeding stuffs are never completely digested by animals, 
as has been shown; only the digestible portions furnish energy for 
physiological uses: the rest is inert matter, passing through the 
animals and of no direct value to them, except possibly in regulat- 
