process; and we
see that the wisdom of the Creator has added to his food the
four-fifths which are wanting, in various forms, as starch, sugar,
&c. with which the animal must be supplied, or his organism will be
destroyed by the action of the oxygen.

It is obvious, that in the system of the graminivora, whose food
contains so small a portion, relatively, of the constituents of the
blood, the process of metamorphosis in existing tissues, and
consequently their restoration or reproduction, must go on far less
rapidly than in the carnivora. Were this not the case, a vegetation
a thousand times more luxuriant than the actual one would not
suffice for their nourishment. Sugar, gum, and starch, would no
longer be necessary to support life in these animals, because, in
that case, the products of the waste, or metamorphosis of the
organised tissues, would contain enough carbon to support the
respiratory process.

LETTER X

My dear Sir,

Let me now apply the principles announced in the preceding letters
to the circumstances of our own species. Man, when confined to
animal food, requires for his support and nourishment extensive
sources of food, even more widely extended than the lion and tiger,
because, when he has the opportunity, he kills without eating.

A nation of hunters, on a limited space, is utterly incapable of
increasing its numbers beyond a certain point, which is soon
attained. The carbon necessary for respiration must be obtained from
the animals, of which only a limited number can live on the space
supposed. These animals collect from plants the constituents of
their organs and of their blood, and yield them, in turn, to the
savages who live by the chase alone. They, again, receive this food
unaccompanied by those compounds, destitute of nitrogen, which,
during the life of the animals, served to support the respiratory
process. In such men, confined to an animal diet, it is the carbon
of the flesh and of the blood which must take the place of starch
and sugar.

But 15 lbs. of flesh contain no more carbon than 4 lbs. of starch,
and while the savage with one animal and an equal weight of starch
should maintain life and health for a certain number of days, he
would be compelled, if confined to flesh alone, in order to procure
the carbon necessary for respiration, during the same time, to
consume five such animals.

It is easy to see, from these considerations, how close the
connection is between