e us some
account of the nature of _milk_.

MRS. B.

True. There are several other animal productions that deserve likewise
to be mentioned. We shall begin with milk, which is certainly the most
important and the most interesting of all the animal secretions.

Milk, like all other animal substances, ultimately yields by analysis
oxygen, hydrogen, carbon, and nitrogen. These are combined in it under
the forms of albumen, gelatine, oil, and water. But milk contains,
besides, a considerable portion of phosphat of lime, the purposes of
which I have already pointed out.

CAROLINE.

Yes; it is this salt which serves to nourish the tender bones of the
suckling.

MRS. B.

To reduce milk to its elements, would be a very complicated, as well as
useless operation; but this fluid, without any chemical assistance, may
be decomposed into three parts, _cream_, _curds_, and _whey_. These
constituents of milk have but a very slight affinity for each other, and
you find accordingly that cream separates from milk by mere standing. It
consists chiefly of oil, which being lighter than the other parts of the
milk, gradually rises to the surface. It is of this, you know, that
butter is made, which is nothing more than oxygenated cream.

CAROLINE.

Butter, then, is somewhat analogous to the waxy substance formed by the
oxygenation of vegetable oils.

MRS. B.

Very much so.

EMILY.

But is the cream oxygenated by churning?

MRS. B.

Its oxygenation commences previous to churning, merely by standing
exposed to the atmosphere, from which it absorbs oxygen. The process is
afterwards completed by churning; the violent motion which this
operation occasions brings every particle of cream in contact with the
atmosphere, and thus facilitates its oxygenation.

CAROLINE.

But the effect of churning, I have often observed in the dairy, is to
separate the cream into two substances, butter and butter-milk.

MRS. B.

That is to say, in proportion as the oily particles of the cream become
oxygenated, they separate from the other constituent parts of the cream
in the form of butter. So by churning you produce, on the one hand,
butter, or oxygenated oil; and, on the other, butter-milk, or cream
deprived of oil. But if you make butter by churning new milk instead of
cream, the butter-milk will then be exactly similar in its properties to
creamed or skimmed milk.

CAROLINE.

Yet butter-milk is very different from common skimmed mil