ot to be understood that
a pound weight of one of these bodies is equivalent to an equal quantity
of the other. During the conversion of starch into fat, the greater
number of its constituent atoms is converted into water and carbonic
acid gas. The greater number of the more important metamorphoses of
organised matter, which take place in the animal organum, is the result
of either oxidation or fermentation: in the conversion of starch or
sugar into fat or oil, both of these processes, it is stated, take
place; a portion of the hydrogen is converted by oxidation into water,
and by fermentation carbonic acid gas is formed, which removes both
oxygen and carbon. Perhaps in the formation of fat fermentation is alone
employed--a portion of the oxygen being removed as water, and another
portion as carbonic acid. The chief difference between the ultimate
composition of starch and fat is, that the latter contains a much larger
proportion of hydrogen and carbon. The knowledge of the exact quantity
of starch required for the formation of a given amount of fat is of
importance in enabling us to estimate the relative feeding value of both
substances. Certain difficulties stand in the way of our acquiring an
accurate knowledge on this point. Not only are there several distinct
kinds of fat, but the precise formula, or atomic constitution of each,
is as yet veiled in doubt. There are three fats which occur in man
and the domesticated animals, and in vegetables. These are stearine,
margarine, and oleine. The relative proportions of these vary in each
animal: thus, in man and in the goose margarine is the most abundant
fat, whilst oleine[9] exists in the pig in a greater proportion than in
man, the sheep, or the ox. The composition of the animal fats does not,
however, vary much; and this fact, together with other considerations,
have led chemists to assume that two-and-a-half parts of starch are
required for the production of one part of the mixed fats of the
different animals. Grape sugar and the pectine bodies--substances which
form a large proportion of the food of the Herbivora--contain more
oxygen and hydrogen than exist in starch, and, consequently, are not
capable of forming so large an amount of fat as an equal weight of
starch. We may assume, then, that 2.50 parts of starch, 2.75 parts of
sugar, or 3 parts of the pectine bodies, are equivalent to 1 part of
fat.

SECTION IV.

RELATION BETWEEN THE COMPOSITION OF AN ANIMAL A