

DEMANDS OF THE BODY FOR NOURISHMENT. 129 
experiments is to the effect that the principal draft will be 
upon the non-nitrogenous materials as long as these last or 
until their quantity is so reduced that the body cannot well 
avail itself of more. Accordingly in these experiments, where 
the energy of the food is deficient, the body loses some protein 
but more fat. 
THE NORMAL, PERMANENT DEMAND. 
The question uow arises: Can the quantities of energy ka- 
tabolized in these experiments be taken as the measure of the 
normal, permanent demand of these men for equivalent mus- 
cular activity? This involves the question of the extent to 
which the body can adapt its consumption of energy to the 
supply in the food, the muscular activity remaining the same. 
It has such a power of adaptation for protein, though just what 
are the circumstances under which it can exercise this adaptive 
power and to what extent and for how long time it can do so, 
the information now available does not tell us. It would seem, 
however, that there must be a more nearly constant ratio be- 
tween muscular activity and the katabolism of energy than 
between such activity and the katabolism of protein. Nor 
would this hypothesis conflict with the theory that the normal 
and permanent demand for protein varies with the intensity of 
the muscular activity.* 
If the above reasoning be correct—and this is not wholly 
certain—the amounts of energy katabolized in the experiments 
_ here reported may be taken as at least approximate indications 
of the normal and permanent requirements of these men for 
corresponding grades of activity. 
In short it would seem probable that the quantities of pro- 
tein katabolized in these experiments are rather small, and the 
quantities of energy more nearly equivalent to those that would 
be permanently required by the same men for normal nutrition 
under the conditions of work and rest similar to those of the 
experiments. But a great deal more experimenting will be 
needed for proof that such is the case. 
The bearing upon dietary standards of these respiration calo- 
rimeter experiments in which the diet was planned to meet 
the needs of the body and its efficiency for this purpose was 

*See Zuntz, U. S. Department of Agriculture, Experiment Station Record, Vol. 
Niles Dr. 530. ° 
