139 
due corrections being- made for water condensed upon the absorbers; 
and (3) the heat equivalent of the muscular work done. 
In the measurements of energy of income and outgo of the body 
the temperature of the interior of the chamber, generally about '20 
degrees, is taken as the basis for computations of the heat removed or 
given off by food, drink, and excretory products in the chamber. a 
(1) The heat carried away by the water current includes (a) the heat 
given off from the skin by radiation and conduction: (b) that brought 
out of the body in the feces and urine and given off in the cooling of 
these excretory products to the temperature of the chamber: (e) that 
brought out of the body in the air. carbon dioxid. and water excreted 
by the lungs and skin and given off in their cooling to the same tem- 
perature: ('/) the latent heat of vaporization of so much of the water 
of c as is permanently condensed on the absorbers (mainly collected as 
drip water); and (e) the heat produced by the transformation of the 
external muscular work. The heat of <u l>. <\ and e finds its way by 
radiation and conduction to the surface of the copper absorbers and 
passes with that of d into the water current by which it is carried out 
of the chamber. 
(2) Although the air current enters and leaves the chamber at the 
same temperature, it carries out more heat than it brings in. The extra 
heat carried out is the latent heat of the water vapor added to the air 
of the chamber by the subject. 13 The amount of this heat is learned 
from the amount of water vapor and its latent heat of vaporization at 
the given temperature. 
(3) The external muscular work is measured and the heat equivalent 
calculated. Before leaving the chamber it is transformed into heat, 
which is carried away by the water current as above stated. 
Energy g iven off in different ways as heat and as external muscular 
work. — The average amounts of energy given off by the body per day 
in the different ways are shown in Table 118. 
The figures in the second column are obtained by subtracting the 
sum of the quantities of heat given off by the feces and urine in cool- 
ing and by the water in condensing on the absorbers and the heat 
equivalent of the external work (b-\-d-\-e above) from the total heat 
taken from the chamber by the water current. Accordingly they rep- 
resent the sum of quantities of heat given off by the skin directly and 
by the product of respiration and perspiration in cooling to the tem- 
perature of the room (a -f- c above). It is hoped that it will be possible 
later to make at least approximate estimates of the latter quantity and 
thus show the amount of heat given off by the skin alone. 
a U. S. Dept. Agr., Office of Experiment Stations Bui. 69, p. 20. 
b The differences in specific heat of the air due to loss of oxygen and gain of carbon 
dioxid are here assumed to be negligible. 
