e advances it will more and more be determined by
reference to the composition of the food.

Although the presence of a sufficient quantity of nutritive compounds in
the food is necessarily the fundamental matter for consideration, its
bulk is scarcely less important. The function of digestion requires that
the food shall properly fill the stomach, and however large the supply
of nutritive matters may be, their effect is imperfectly brought out if
the food is too small in bulk, and it actually may become more valuable
if diluted with woody fibre, or some other inert substance. At first
sight this may appear at variance with the observations already made as
to the effects of woody fibre in protecting the nutritive matters from
absorption; but practically there are two opposite evils to be contended
against, a food having too small a bulk, or one containing so large a
proportion of inert substances as to become disadvantageously
voluminous. The most favourable condition lies between the two extremes,
and the natural food of all herbivorous animals is diluted with a
certain amount of woody fibre. When these are replaced by substances
containing a large quantity of nutritive matters in a small bulk, the
result is that the natural instinct of the animal causes it to continue
feeding until the stomach is properly distended, and it consequently
consumes a much larger quantity of food than it is capable of digesting,
and a more or less considerable quantity passes unchanged through the
intestines, and is lost. On the other hand, if the food be too bulky,
the sense of repletion causes the animal to cease eating long before it
has obtained a sufficient supply of nutritive matter. It is most
necessary, therefore, to study the mixture of different kinds of food,
so as to obtain a proper relation between the bulk and the nutritive
matters contained in the mixture; and on examining the nature of the
mixed foods most in vogue among feeders, it will be found that a very
bulky food is usually conjoined with another of opposite qualities.
Hence it is that turnips, the most voluminous of all foods, are used
along with oil-cake and bean-meal, and if from any circumstances it
becomes necessary to replace a large amount of the former by either of
the latter substances, the deficient bulk must be replaced by hay or
straw.

It has been already remarked that there are three great purposes to
which the food consumed is appropriated; the increas