ae 
HXPERIMENTS ON DIGESTION OF FOOD BY MEN. Ay be 
This experiment is of interest because of the unusual care 
and thoroughness with which the details were carried out by 
the gentlemen who joined in the work; because it gives a very 
accurate measure of the digestibility of the nutrients of an 
ordinary mixed diet under normal condition, and because it 
adds to the list of accurate observations upon the actual food 
consumption of typical persons. 
COMMENTS UPON THE TABLES. 
Some of the data above tabulated call for a few words of 
explanation before we proceed to the summarizing of the results. 
Fuel values.—The fuel values of the digested food may be 
estimated either from the heats of combustion as found by 
determinations with the bomb calorimeter or by the use of 
factors such as those of Riibner. ‘The latter, as commonly 
used, apply to total rather than digestible nutrients and ascribe 
4.1 calories to each gram of protein or carbohydrates and 9.3 
calories to each gram of fats. 
In the experiments here reported the heats of combustion of 
both food and feces were determined by direct combustion with 
oxygen in the bomb calorimeter. In experiments 11-14 inclu- 
sive the heats of combustion of the dried residue of the urine 
were determined in like manner. 
It is hoped that a somewhat detailed, discussion of the 
methods of estimating fuel values from the heats of combus- 
tion may be given in another place. Meanwhile it will sufhce 
to explain briefly the methods of computation used for the 
preceding tables. 
Net fuel value of food digested.—By subtracting the heat of 
combustion of the feces from that of the total food eaten we 
obtain the total heat of combustion of the food digested. 
This, however, does not represent the actual fuel value. In 
the first place it is not positively proved that the energy lib- 
erated and used in the body is exactly the same as that devel- 
oped in the form of heat by combustion with oxygen in the 
calorimeter. It is common, however, to assume that such is 
the case. Even on this assumption the fuel value of the 
digested food will not be exactly the heat of combustion 
because not all of the digested food is completely consumed in 
the body. Leaving out of account the material which is either 
