There is no mystery about this choice; its rules are well known,
but I think we ought probably to pay more attention to the age of
the milk as well as its quality. The first milk is watery, it must
be almost an aperient, to purge the remains of the meconium curdled
in the bowels of the new-born child. Little by little the milk
thickens and supplies more solid food as the child is able to
digest it. It is surely not without cause that nature changes the
milk in the female of every species according to the age of the
offspring.

Thus a new-born child requires a nurse who has recently become mother.
There is, I know, a difficulty here, but as soon as we leave the
path of nature there are difficulties in the way of all well-doing.
The wrong course is the only right one under the circumstances, so
we take it.

The nurse must be healthy alike in disposition and in body. The
violence of the passions as well as the humours may spoil her milk.
Moreover, to consider the body only is to keep only half our aim
in view. The milk may be good and the nurse bad; a good character
is as necessary as a good constitution. If you choose a vicious
person, I do not say her foster-child will acquire her vices, but
he will suffer for them. Ought she not to bestow on him day by
day, along with her milk, a care which calls for zeal, patience,
gentleness, and cleanliness. If she is intemperate and greedy her
milk will soon be spoilt; if she is careless and hasty what will
become of a poor little wretch left to her mercy, and unable either
to protect himself or to complain. The wicked are never good for
anything.