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CONSERVATION OF ENERGY IN LIVING ORGANISM. 107 
great deal of muscular work going on within his body. Even 
when he is asleep the organs of respiration, circulation and di- 
gestion are active. The energy of the internal work is trans- 
formed into heat in the body and leaves the body as heat. This 
is proven by the fact, explained beyond, that when the body is 
at rest the heat it gives off is equal to the potential energy 
(heat of oxidation) of the material oxidized in the body. 
When the man is working the bicycle, part of the power 
which he applies to the pedals is transformed into the heat of 
friction of the machine, but the larger part is transformed into 
electrical energy by means of a dynamo connected with the 
bicycle. The electrical current thus produced by the bicycle- 
dynano passes through a lamp and is converted into heat. In 
this way all of the external muscular work done, z. e., all the 
power applied to the pedals, is transformed into heat within 
the chamber. Arrangements are made for measuring the heat 
of friction and also the electrical current produced by the bi- 
cycle-dynamo. The latter therefore serves as an ergometer for 
measuring the external muscular work. 
We warm our houses in winter by a current of hot water 
which passes through radiators by which the heat is radiated 
into the rooms. We may hereafter learn to cool them in sum- 
mer by the opposite process, z. ¢., by passing cold water 
through the pipes and making them absorbers, so that the water 
will carry away the heat. Precisely this is done in the respira- 
tion calorimeter. A copper pipe passes around the chamber 
close to the walls; through this flows a current of cold water 
and by regulating the temperature and rate of flow of the water 
current, the heat is absorbed and carried out of the chamber 
as fast as generated. The temperature within the chamber 
is thus kept at a point agreeable to the subject and remains 
almost absolutely constant—indeed the variations are often ~ 
within a single degree during the whole twenty-four hours. 
The diet during the experiment is uniform from day to day. 
All food and drink passed into the chamber, and all solid and 
liquid excreta passed out, are carefully weighed, sampled and 
analyzed. By comparing the chemical elements and com- 
pounds received by the body in food, drink and inhaled air 
