
CONSERVATION OF ENERGY IN LIVING ORGANISM. 109. 
The potential energy of the food and excretory products is 
measured by the amount of heat generated when these sub- 
stances are burned outside the body, that is by their heats of 
combustion, as learned by burning them with oxygen in an 
apparatus called the bomb calorimeter. "The measurements of 
the kinetic energy given off from the body are made by means 
of the respiration calorimeter. The principle used in the meas- 
urement of energy by the respiration calorimeter is this. In 
the rest experiments, practically all the kinetic energy leaves 
the body as heat. In the work experiments part is put forth 
as muscular power applied to the pedals of the bicycle-dynamo, 
which transforms this external muscular energy into heat and, 
as an ergometer, measures its amount. ‘The problem is to 
measure the whole heat including that which left the body as 
heat and that which resulted from the transformation of the 
muscular work. ‘The method consists in collecting this heat 
for measurement, and at the same time providing that there 
shall be no gain or loss in the amount. 
The chamber of the calorimeter is enclosed by double metal 
walls, which are surrounded on all sides by walls of wood with 
air spaces between, so that the temperature within the chamber 
is not appreciably affected by changes in the temperature of the 
room outside. Very delicate electrical devices show changes in 
the temperature of the metal walls; and devices for heating and 
cooling the walls are arranged so that their temperature may 
be kept as near that of the interior of the chamber as desired, 
and the very small amounts of heat that may pass through them 
into or out of the calorimeter may be made to counterbalance 
each other. ‘The temperature of the ventilating air current is 
also regulated so that neither more nor less heat is taken in than 
is brought out. Accordingly there is no gain or loss of heat 
either through the walls of the chamber or by the ventilating 
air current. The heat produced within the chamber is that 
from the energy of the material oxidized in the man’s body. 
The only way this heat can escape is by the proper agencies for 
carrying it out and measuring it. 
These agencies are two, water vapor and the cold water cur- 
rent. A small portion of the heat generated within the cham- 
ber is carried out by water vapor in the ventilating air current. 
