| | substance.
---------------------+--------+-----------+-----------+----------------
Average of 98 oxen | 1.47 | 7.69 | 66.2 | 75.4
Average of 348 sheep | 1.80 | 7.13 | 70.4 | 79.53
Average of 80 pigs | 0.44 | 6.44 | 71.5 | 78.40
---------------------+--------+-----------+-----------+----------------

The quantity of food consumed daily by an animal is, as might be expected,
proportionate to the weight of its body. The pig consumes, for every 100
lbs. of its weight, from 26 to 30 lbs. of food, the sheep 15 lbs., and
the ox 12 to 13 lbs. These figures and the statements which I have made
relative to the proportions of fat and plastic elements in the animals'
bodies, apply to them in their fattening state, and when the food is
of a highly nutritious character. The calf and the young pig will
make use--to cause their increase--of a larger portion of nitrogenous
matters. The sheep, however, being early brought to maturity, will, even
when very young, store up the plastic and non-plastic constituents of
its food, in nearly the same relative proportions that I have mentioned.

As it is the food taken into the body that produces heat and motion, it
might at first sight appear an easy matter to determine the amount of
heat or of motion which a given weight of a particular kind of food is
capable of producing within the animal mechanism. But this performance
is not so easy a task as it appears to be. In the first place, all of
the food may not be perfectly oxidised, though thoroughly disorganised
within the body; secondly, as animals rarely subsist on one kind of
food, it is difficult, when they are supplied with mixed aliments, to
determine which of them is the most perfectly decomposed. But though the
difficulties which I have mentioned, and many others, render the task
of determining the nutritive values of food substances difficult, the
problem is by no means insoluble, and, in fact, is in a fair way of
being solved. Professor Frankland, in a paper published in the number
of the _Philosophical Magazine_ for September, 1866, determines the
relative alimental value of foods by ascertaining the quantity of heat
evolved by each when burned in oxygen gas. From the results of these
researches he has constructed a table, showing the amount of food
necessary to keep a man alive for twenty-four hours. The following
figures, which I select from this table, are of int