h a manner that its weight remains constant,
a balance is produced between the supply of nutriment contained in the
food and the waste of the tissues, the gain from the former exactly
counterpoising the loss occasioned by the latter. If in this state of
matters an additional supply of food be given, this balance is deranged,
and the nutriment being in excess of the loss, the animal gains weight,
and it continues to do this for some time, until it reaches a point at
which a new balance is established, and its weight again becomes
constant; and this is due to the fact that the animal becomes subject to
an additional waste, consequent on the increased weight of matter
accumulated in its tissues. If, after the animal has attained its new
constant weight, the food be a second time increased, a further gain is
obtained, and so on, with every addition to the supply of nutriment,
until at length a certain point is reached, beyond which its weight
cannot be forced. In fact, each successive increase of weight is
obtained at a greater expenditure of food. If, for example, a lean
animal is taken, and its food increased by a given quantity, it will
rapidly attain a certain additional weight, but if another extra supply
of food be given, the increase due to it will be much more slowly
attained, and so on until at length an additional increase can only be
secured by the long-continued consumption of a very large quantity of
food. The great object of the feeder is to obtain the greatest possible
increase with the smallest expenditure of food, and to know the point
beyond which it is no longer economical to attempt to force the process
of fattening. To do this it is necessary first to consider the
composition of the animal itself, then that of its food, and lastly, the
mode in which it may be most economically used.

It has been already observed that the animal tissues are composed of
albuminous or nitrogenous compounds, fat, mineral matters, and water;
but the proportions of these substances have, until lately, been very
imperfectly known. Water is well known to be by far the largest
constituent, and amounts in general to about two-thirds of the entire
weight, and it has been generally supposed that the nitrogenous matters
stood next in point of abundance, but a most important and elaborate
series of experiments by Messrs. Lawes and Gilbert have shewn that they
are greatly exceeded by the fatty matters. The following table contains
a s