THE CONSERVATION OF ENERGY IN THE ANIMAL BODY. 263 
still adhered to the unity and simplicity of the combustion theory, 
but in general various subsidiary hypotheses were brought in to 
account for the observed surplus, such as the motion of the blood, 
friction, imbibition, etc. 
RuBNEr’s ExperRIMeNts.—The demonstration of the law of the 
correlation and conservation of energy in the inorganic world sup- 
plied the clue to a rational explanation of the energy manifestations 
in the living organism, while the subsequent developments of thermo- 
chemistry served also to demonstrate a material source of error in 
the older experiments on animals. In those experiments the com- 
puted heat production was based upon the amounts of carbon and 
hydrogen oxidized and the heats of combustion of those elements, 
the nitrogenous compounds not being considered. The body, how- 
ever, does not oxidize free carbon and hydrogen, but various organic 
compounds, while among its excreta are likewise incompletely 
oxidized bodies. The computed heat production, therefore, in the 
early experiments could not fail to be seriously erroneous. From 
the new point of view, therefore, there appeared no reason to seri- 
ously doubt that the animal heat has its sole source in the metab- 
olism of food and tissue, or, in other words, that the law of the con- 
servation of energy applies to the animal body. The first to under- 
take an experimental demonstration of this fact by modern methods 
was Rubner.* 
His object being primarily to investigate the source of animal 
heat, his experimental method could be somewhat abbreviated from 
the general method outlined on p. 260. No external mechanical 
work having been done by the animals, we have Case 3 of the 
four possible ones there mentioned. If we let. 
F=potential energy of food, 
E= . «© excreta, 
G= 6 «gain by body, 
H=heat produced, 
then, assuming the initial and final states of the body to be the same, 
we have 
F=E+G+4H, 
* Zeit. f. Biol., 30, 73. 
