LIFE: ITS ORIGIN AND NATURE 37 
energy, and as such subject to the law of con¬ 
servation. We have already touched upon this 
question, briefly, in the chapter dealing with the 
origin of life. 
There is undoubtedly an equivalence which 
can be roughly measured between the energy- 
content of food consumed, and the energy ex¬ 
pended by the body in its various activities. The 
analogy usually employed is that of the steam 
engine. Here a certain amount of coal (fuel) 
is consumed, which supplies a certain amount 
of heat and energy during its combustion. 
Similarly, it is claimed, a certain amount of 
fuel (food) is supplied to the human body, and 
heat and energy are likewise imparted during 
the period of its oxidation and combustion. 
This equivalence has been proved to exist in 
the human body by means of an instrument 
known as a “calorimeter.” The living subject 
is inclosed within a small cabin-like space, 
and the heat and energy output of the body 
are accurately measured by means of delicate 
registering instruments, the amount of carbon 
dioxide, heat, etc., being thus determined. 
The usually accepted view is that the latent 
energy of the food is imparted to the body, 
which expends it in various internal and ex¬ 
ternal nervous and muscular activities. There 
is, however, an Alternative theory, which may 
be advanced, and which has in fact been de¬ 
fended by the present writer and others, which, 
while it accepts the admitted facts of equiva¬ 
lence, contends that the relationship in question 
(between food and bodily energy) is not that of 
cause and effect, but mere equivalence. 
