
DEMANDS OF THE BODY FOR NOURISHMENT. ° I4I 
amounts are best for an average individual of a given class. 
Such data as I have been able to gather seem to me now to 
favor the common belief that the need of protein in the diet 
increases with the intensity as well as the total amount of 
muscular, if not mental, work, and nothing could be clearer 
than the testimony both of common experience and of the ex- 
periments here reported, regarding the increase of metabolism 
- of material and energy in the body with increase of muscular 
activity. 
It will not be out of place here to give a word of warning 
regarding the not uncommon practice of basing general theories 
of nutrition upon the results of special experience. There are 
abundant instances of people eating very large quantities of 
food without excessive muscular exercise and maintaining 
health and strength for many years. No less common are the 
cases in which ‘‘ very small eaters’’ maintain a high degree of 
physical and mental activity and the best of health until old 
age. But it would be hardly justifiable to take the experience 
of either the one class or the other as a measure for a general 
dietary standard. 
ESTABLISHING OF DIETARY STANDARDS. INQUIRY NEEDED. 
The establishment of dietary standards is not a simple mat- 
ter. If, for instance, we endeavor to formulate quantities of 
protein and energy appropriate for a man with a small, medium 
or large amount of muscular work, not only do we lack the 
exact measure of the activity, but no data to show either the 
range of variation or the average actual demand for any given 
grade of activity are available. We can do simply what has 
been done by numerous investigators, observe the kinds and 
amounts of food that are actually eaten by people whom we 
regard as well nourished, compare the results with those of 
more or less exact feeding experiments, metabolism experi- 
ments and others, with persons having different amounts of 
food under different conditions of work and rest, and then con- 
tent ourselves with such general estimates as seem to have the 
highest grade of probability in their favor. But no one knows 
how nearly correct they are for people of a given class or how 
close they come to the measure of the actual needs of any given 
individual of that class. 
