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DEMANDS OF THE BODY FOR NOURISHMENT. 139 
MUSCULAR ACTIVITY AND THE DEMAND FOR NUTRIMENT. 
I am here laying much stress upon muscular activity as in- 
creasing the demand for nutriment. The principle is perfectly 
simple and perfectly well understood. Every feeder of horses 
or oxen appreciates its force and applies it in his feeding prac- 
tice; but most of us fail to realize that the principle is as valid 
for man as it is for the lower animals, and we are apt to eat 
what we like without much regard to our physiological needs. 
The case is affected in a peculiar way by a fact to which not all 
of us have given due consideration. Generally speaking smaller 
incomes go with manual and larger with mental labor. In other 
words the well-to-do not only have all they want to eat but their 
food is apt to be such as to tempt the appetite, so that while 
they really need less food than their neighbors with less money 
and harder manual work, they are unconsciously led to eat as 
much or more. 
INDIVIDUALITY, HABIT AND MUSCULAR ACTIVITY. 
Comparison of the results of dietary studies and metabolism 
experiments, including those with the respiration apparatus 
and the respiration calorimeter, has led me to believe that the 
actual needs of the body are more largely affected by the three 
factors, habit, the personality of the individual and the degree 
of muscular activity, than has always been appreciated, and I 
have in previous discussions of the subject felt it important to 
insist upon three things: 
First; that no standard for a given class can be more than _ 
the expression of an average demand, from which the needs of 
individual persons of the class may vary widely. 
Second; that the data now at hand do not suffice for at all 
accurate statements of the average demand for any given class. 
‘The current standards are therefore, at best, tentative, more or 
less crude, and subject to revision as data accumulate. 
fihirds that the facts at hand suffice to warrant the belief 
that for many if not most people with sedentary and intellec- 
tual occupations as distinguished from active muscular labor, 
comparatively small amounts of food are sufficient and more 
healthful than such quantities as are needed by manual labor- 
ets, and are actually eaten by many people not engaged in 
manual work. : 
