72 STORRS AGRICULTURAL EXPERIMENT STATION. 
3. Protect the materials of the body or of other food from 
consumption by being oxidized; in other words, to:— 
a. Protect protein of the body or of food from oxidation. 
b. Protect fats (and carbohydrates) from oxidation. 
We may also distinguish between what might be called the 
physical and the physiological fuel value. ‘The physical fuel 
value would be the total energy made kinetic in the body, and 
would be measured by the heat of oxidation of the material 
burned, The physiological fuel value would be represented 
by the actual benefit gained by the body from the use of the 
fuel for the different purposes which it serves. Thus the 
actual value to the body of the energy from a gram of fat may 
be, and is by some physiologists held to be, less when used for 
mechanical work than if used as heat. To what extent the 
physiological and the physical fuel values agree or disagree is 
not yet known. For the present: purpose the term fuel value 
is here applied to the physical value. 
DEFINITIONS. 
What has thus been explained may be summarized in the 
following definitions. 
Digestibility.—This term is used to designate the quantity or 
percentage of a given amount of food or of a given nutrient 
which is digested, z. ¢., rendered capable of absorption, and, 
under normal IGSCRS. actually absorbed from the une 
tary canal. 
Avatlability.—This term is used to designate the quantity or 
percentage of a given amount of food or of a given nutrient 
which is capable of being utilized for the forming of tissue and 
yielding energy. It is the total material less the corresponding 
material of the feces. 
fuel value.—By this is understood the energy (heat of com- 
bustion) of the material of the food which is oxidized, 7. e. 
capable of oxidation in the body. For the total food it is the 
total energy less that of the corresponding unoxidized mate- 
rials of the feces and urine. For the protein it is likewise the 
total heat of combustion less that of the corresponding unoxi- 
dized residues of these excretions. For the fats and carbohy- 
drates it is the total energy less the energy of the corresponding 
unoxidized material of the feces. 

, a eee. 
