blue instead of a rosy tint of
lips and fingertips, as though perished with cold. The babe wakes on
being disturbed, and gives a faint short cry of distress; the livid hue
of its surface deepens, it struggles feebly, its mouth twitches as
though convulsions might be coming on. Soon, however, these symptoms
subside, the babe smiles again, is cheerful, and save for the tints of
its face and lips, it looks like other infants, but frailer.

This condition has a name in medical writings, from a Greek word
expressive of the blue tint which characterises it, and is called
_cyanosis_. It depends on the blood not having undergone completely
those changes in the lungs which take place in the healthy state. The
blood, as it returns through the veins to the right side of the heart,
is of a deep purple hue. The right side of the heart contracting sends
it to the lungs, where, in the minute vessels of the air-cells, it is
purified, and returns vivified by the oxygen a bright scarlet stream, to
be distributed by the arteries over the whole body; and thence to return
once more for fresh purification to the right side of the heart. Before
birth, the blood does not run the same course, but is purified within
the mother's body, the blood running through channels which close with
the first breath the infant draws. The previously existing communication
between the two sides of the heart ceases at the same time as the new
channels are opened, by the shutting of a thin valve which had hitherto
allowed the blood to pass from one side to the other.

Sometimes this closure fails to take place, or takes place but
imperfectly; sometimes, in addition, the channels which should be
disused after birth remain open still; and sometimes also the heart is
otherwise imperfectly formed, and a large communication exists between
the two sides of the heart, which long before birth ought to have been
firmly partitioned off from each other.

According to the freedom of communication between the two sides of the
heart, there is more or less ready intermingling of the impure blood
with that which is already purified; and this is betokened by the
greater or less severity of the symptoms which I have described. When
the heart is very malformed, and the blood consequently is very impure,
life is but a short agony which ends in a few weeks; some slight
movement, some little accidental cold deranging altogether the imperfect
machinery, and bringing it to a sudden st