l is heated in proportion.

Thus we see that food has another function besides that of forming
animal matter, namely to supply heat. When the food does not contain a
sufficient quantity of starch, sugar, etc., to answer the demands of
the system the _animal's own fat_ is carried to the lungs, and there
used in the production of heat. This important fact will be referred to
again.

FOOTNOTES:

[G] By _proximate principle_, we mean that combination of vegetable
elements which is known as a vegetable product, such as _wood_, etc.

[H] _Muscle_ is _lean meat_, it gives to animals their strength and
ability to perform labor.

[I] This, of course, supposes that the soil is fertile in other
respects.

CHAPTER VII.

LOCATION OF THE PROXIMATES AND VARIATIONS IN THE ASHES OF PLANTS.

[Of what proximate are plants chiefly composed?

What is the principal constituent of the potato root?

Of the carrot and turnip?

What part of the plant contains usually the most nutriment?]

Let us now examine plants with a view to learning the _location_ of the
various plants.

The stem or trunk of the plant or tree consists almost entirely of
_woody fibre_; this also forms a large portion of the other parts except
the seeds, and, in some instances, the roots. The roots of the potato
contain large quantities of _starch_. Other roots such as the _carrot_
and _turnip_ contain _pectic acid_,[J] a nutritious substance resembling
starch.

It is in the _seed_ however that the more nutritive portions of most
plants exist, and here they maintain certain relative positions which
it is well to understand, and which can be best explained by reference
to the following figures, as described by Prof. Johnston:--

[Illustration: Fig. 1.]

"Thus _a_ shows the position of the oil in the outer part of the
seed--it exists in minute drops, inclosed in six-sided cells, which
consists chiefly of gluten; _b_, the position and comparative quantity
of the starch, which in the heart of the seed is mixed with only a small
proportion of gluten; _c_, the germ or chit which contains much
gluten."[K]

[Is the composition of the inorganic matter of different parts
of the plant the same, or different?

What is the difference between the ash of the straw and that of the
grain of wheat?]

The location of the _inorganic_ part of plants is one of much interest,
and shows the adaptation of each part to its particular use. Take a
wheat plant, for inst