the requirements of the body on a purely vegetarian diet. Experience
has shown, however, that it is both natural and advantageous that we
employ a mixed diet.

The property of protein to build living tissue and replace tissue
waste probably depends upon several factors; but certainly one of
them is the presence of nitrogen. So intimately associated are the
consumption of the tissue substance and the elimination of nitrogen
that we have no better way of judging the amount of tissue substance
used in the body than by determining the quantity of nitrogen that
appears in its various waste products. From such investigations it
has been found that the quantity of protein required to repair the
breaking down of the tissues is not great. The average man consumes
approximately a quarter of a pound (100 to 120 grams) of protein
daily; but this quantity is in excess of his real needs. Indeed,
Chittenden has shown that for various classes of individuals, namely,
students, athletes and soldiers, half as much is sufficient. Other
physiologists, though admitting that this is true, contend that it is
inadvisable to regulate one's diet on such a slender basis. Very good
reasons are assigned for the view that more protein is needed than
just enough to counterbalance the tissue waste. Thus, in the case of
animals, it has been found that a diet low in protein finally causes
digestive disturbances and other ailments.

Although it does not seem advisable to practise rigid economy in
arranging the protein content of the diet, it is equally important
that we should not go to the other extreme. The consumption of over-
large quantities of protein, as would be the case if we lived
exclusively upon meat, increases putrefaction in the intestines and
throws unnecessary work upon the kidneys, which are the organs