

RESPIRATION CALORIMETER AND EXPERIMENTS. 239 
even though the data of the experiments have not all the com- 
pleteness that is to be desired. 
In the experiments here described the energy of outgo 
includes both the heat given off from the body and, in one case, 
that of a considerable amount of external muscular work. 
The income and outgo agree as closely perhaps as could be 
expected in view of the possible sources of error. 
In experiment No. 9, the disagreement is about as large as 
in the average of the later and more accurate experiments. 
The income here exceeds the outgo by about 25 calories per 
day. This quantity is really quite small. It would corre- 
spond to the potential energy of about one-tenth of an ounce 
of body fat, or nearly the same weight of butter, or one-fourth 
of an ounce of sugar, or one-third of an ounce of bread. 
It may be that a small part of the energy which is trans- 
formed in the body is given off in some form which the appa- 
_tatus and methods here used are incapable of measuring. It is, 
for instance, conceivable that intellectual activity may be ac- 
companied by the evolution of energy in some other form than 
heat. These, however, are matters of speculation. 
We should, of course, be unwarranted in assuming that 
these experiments completely demonstrate the action of the 
law of the conservation of energy in.the human organism. 
They do, however, seem to us to be reasonably near to such 
demonstration, for the cases in which they were made. 
USE OF THE PRINCIPLE IN FURTHER RESEARCH. 
It is certainly safe to assume that the principle is correct, 
and the apparatus and methods are accurate to the degree 
required for the experimental study of a large variety of the 
fundamental problems of biological chemistry and physics. 
Among these are the metabolism of energy and the production 
of heat by the body in the performance of its ordinary func- 
tions, as circulation, respiration and digestion; the relations of 
muscular and mental work to the metabolism of matter and 
energy; the demands of the body for nutriment under different 
conditions of work and rest; the duties performed by the dif- 
ferent nutrients of food in supplying the needs of the body; 
and finally, the nutritive values of food materials and the 
amounts and proportions best adapted to the needs of the people 
