

CONSERVATION OF ENERGY IN LIVING ORGANISM. Os Bie 
The figures for income and outgo of energy require a word 
of explanation. A distinction is here made between the total* 
income, which is represented by the potential energy of the 
food, and the net income, which is the energy of the material 
actually oxidized in the body. ‘This energy of net income is 
represented by the available energy of the nutrients of the 
food (2. ¢., potential energy of total food less that of the urine 
_ and feces) minus the potential energy of the material gained 
or plus that of material lost by the body when the latter is not 
in nitrogen and carbon equilibrium. The total energy of outgo 
would be the kinetic energy given off from the body in heat 
and as external muscular work plus the potential energy of the 
unoxidized materials in the urine and the feces. ‘The net en- 
ergy of outgo consists of the heat given off and the external 
muscular work done. The balance of income and outgo is best 
shown by the net rather than by the total quantities, as is the 
case in Table 18. 
It is to be remembered that the figures for net income of 
energy represent the heat of combustion of the material ac- 
tually oxidized. ‘This material consists mainly of the digest- 
ible portion of the food of which the amount and heat of 
combustion are found by direct determination. ‘To its heat of 
combustion is added that of the material lost, or from it is sub- 
' tracted that of the material gained by the body. The amounts 
of materials gained or lost are determined from the gain or loss 
of nitrogen and carbon, and their heats of combustion are cal- 
culated by the use of factors based upon direct determination 
of the heats of combustion of similar substances. The figures 
for net outgo are the results of direct experimental measure- 
ment. In other words, the net income of energy is mainly 
and the net outgo entirely the results of direct determinations. 
A common usage is followed in applying the term ‘‘potential 
energy’’ to the energy latent in the food and body material 
oxidized. Whether chemical energy would or would not be a 
more correct expression no attempt is here made to decide. 
Ordinary usage is also followed in expressing potential energy in 
terms of heat—z. ¢., as calories—thus employing a unit of kinetic 
energy for the measurement. ‘This though unsatisfactory is 

* The terms ‘‘total”? and “net”? here applied to income and outgo of material and 
energy are used for present convenience, and may in future reports be replaced by 
more satisfactory expressions. 
