a
limited meat supply. To some of us this may seem a hardship.
Meat, however, is by no means the essential that we have been
wont to suppose and partial deprivation of it is not
inconsistent with high bodily efficiency. Certainly no
patriotic citizen would wish to insist on his customary
allowance of roast pig at the cost of the food supply of his
brothers in the trenches.

[2] "Roast Pig," _Science_, 1917, xlvi, 160.

The United States Department of Agriculture has estimated that a pig
that has reached the weight of 150 pounds should be slaughtered, because
beyond that weight the cost of the quantity of feed required to maintain
the animal is out of proportion to the gain in food value of the pig.
One might, therefore, call a pig weighing 150 pounds a _maximal economic
hog_.

II

CALORIES IN COMMON LIFE

A person is properly nourished who receives adequate energy in the form
of carbohydrate and fat (and incidentally protein); adequate material
for repair of wornout parts, such as protein and mineral salts; and the
diet must contain certain accessory food substances known as food
hormones or "vitamins." Also, it must contain water. But this is not
all, for the food offered must be acceptable to the palate of the
individual. A member of the French Scientific Commission which visited
the United States in the summer of 1917, when questioned regarding the
use of corn bread in France, replied "on ne peut pas changer des
habitudes." The proper nutrition of an individual depends, therefore,
not only upon a sufficient supply of food from a mechanistic standpoint,
but also upon the reasonable satisfaction of the sense of appetite.
These dual fundamentals of proper nutrition should be ever borne in
mind.

Heat from the sun enters into the composition of the food substances
when they are being built up in the plants, and this energy, which is
latent in the food, is set free in the animal body and is used as the
source of power behind all the physical activities of the body. The
energy can all be recovered as heat and measured in the form of
calories. According to the principles of the law of the conservation of
energy, heat is not destructible. The understanding of the value of a
calorie is indispensable for the comprehension of nutrition. A calorie
is the measure of a unit of heat, or the quantity of heat necessary to
raise a liter of water from 0 deg. to 1 deg. Centigrade. Apparatus has
bee