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932 METABOLISM.
V. THE NECESSITY OF FOOD BY MAN UNDER VARIOUS CONDITIONS.
Various attempts have been made to determine the daily quantity of
organic food needed by man. Certain investigators have calculated
from the total consumption of food by a large number of similarly fed
individuals—soldiers, sailors, laborers, etc. —the average quantity of
foodstuffs required per head. Others have calculated the daily demand
for food from the quantity of carbon and nitrogen in the excreta, or cal-
culated it from the exchange of force of the persons experimented upon.
Others, again, have calculated the quantity of nutritive material in a
diet by which an equilibrium was maintained in the individual for one or
several days between the consumption and the elimination of carbon
and nitrogen. Lastly, still others have quantitatively determined, dur-
ing a period of several days, the organic foodstuffs daily consumed by
persons of various occupations who chose their own food, by which they
were well nourished and rendered fully capable of work.
Among these methods a few are not quite free from objection, and
others have not as yet been tried on a sufficiently large scale. Neverthe-
less the experiments collected thus far serve, partly because of their
number and partly because the methods correct and control one another,
as a good starting-point in determining the diet of various classes and
similar questions.
If the quantity of foodstuffs taken daily be converted into calories
produced during physiological combustion, we then obtain some idea of
the sum of the chemical energy which under varying conditions is intro-
duced into the body. It must not be forgotten that the food is never
completely absorbed, and that undigested or unabsorbed residues are
always expelled from the body with the feces. The gross results of calo-
ries calculated from the food taken must therefore, according to Rubner,
be diminished by at least 8 per cent. This figure is true at least when
the human being partakes of a mixed diet of about 60 per cent of the
proteins as animal, and about 40 per cent of the proteins as vegetable
foodstuffs. With more one-sided vegetable food, especially when this
is rich in undigestible cellulose, a much larger quantity must be sub-
tracted.
The following summary contains a few examples of the quantity of
food which is consumed by individuals of various classes of people under
different conditions. In the last column we also find the quantity of
living force which corresponds to the quantity of food in question, calcu-
lated as calories, with the above-stated correction. The calories are
therefore net results, while the figures for the nutritive bodies are gross
results.
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