
os ae Byte BAN no) 
ae 
et tars 
EXPERIMENTS ON METABOLISM OF ENERGY. aC 7 
2. The quantities of nutrients and energy metabolized by 
men under different conditions of rest and muscular and men- 
tal exercise. | 
3.. The amounts of material and energy required for inter- 
nal physiological work, as that of digestion, circulation and 
respiration. 
4. The relation between external muscular work and the 
nutrients and energy metabolized in its performance. This 
general problem includes the narrower one of the power of the 
body as a machine to convert the potential energy of its food 
and of its previously stored material into muscular energy. 
Viewed from one standpoint this latter phase of the subject is 
the same as that to which the expression ‘‘’The animal body as 
a prime motor’’ is frequently applied. From another stand- 
point it includes the comparison of the animal body with steam 
engines and other sources of power in respect to the economy 
with which the energy of fuel is utilized; the fuel in the case 
of the animal being its food, while in the case of the ordinary 
machine it is coal, or oil, or wood. 
5. The transformations of nutrients and energy in mental 
work. | 
6. The capacities of the different classes of nutrients to 
supply the body with material and energy; the proportions in 
which they may replace each other in building tissue or yield- 
ing energy as heat or as work; and their power to protect each 
other and the materials of the body from consumption. 
7. The kinds and amounts of nutrients required for nour- 
ishment of people of different classes and in different conditions 
in life, the nutritive values of food materials and the fitting of 
food to the needs of the consumer. 
Of the above problems all have been studied to a greater or 
less extent already except No. 5, which has to do with food 
and mental work. It is hoped that the study of this latter 
problem may also be entered upon in the not too distant future. 
Besides the problems thus detailed a number of others have 
received attention. Among these are: 
8. The digestion and assimilation of food materials. 
9. The quantities of carbon dioxid, water, nitrogen, and 
other materials excreted by the body, as well as the energy 
- given off as heat and as external muscular work under different 
