rather more than sixty years ago a German physician discovered that air
had entered the lungs but imperfectly; that perhaps a third, perhaps
even as much as half, of the lungs had never been dilated, but had
remained solid and useless; that in consequence the blood was but
half-purified, and vitality therefore but half-sustained. The lungs,
however, were found to have undergone no real change; they were not
diseased, but if air was blown into them the dark solid patches sunk
below the level of the surrounding substance, expanded, grew bright in
colour and like a sponge from which the water has been squeezed, and
crackled, or crepitated as the technical term is, from the air contained
within them.

We breathe in health so without conscious effort that we never realise
the fact that, according to the calculation of most competent observers,
the mere elasticity of the lungs, independent even of the elasticity of
the chest walls, opposes a resistance to each inspiration equal to 150
pounds avoirdupois in the grown man and 120 in the grown woman. The want
of breath puts the respiratory muscles into play: the man takes a deep
inspiration, and by this unconscious effort, he overcomes the resistance
of the chest and the elasticity of the lungs. The new-born infant feels
the same want and makes the same effort; but its muscular power is
small, and its inspirations are often so feeble as to draw the air in
some parts only into the larger tubes, while many of the smaller remain
undilated, and much of the lung continues in the state in which it was
before birth. The blood being thus but imperfectly purified, all the
processes of nutrition go on imperfectly, the vital powers languish, the
inspiratory efforts become more and more feeble, while the elasticity of
the lung is constantly tending to empty the small cells of air and to
oppose its entrance, and next the temperature sinks and the infant dies.

Cases in which this condition of the lungs exists usually present the
history of the child from the very first having failed to utter a strong
and loud cry like that of other children. Even after breathing has gone
on for some time, such children usually appear feeble, and they suck
with difficulty, although they often make the effort. An infant thus
affected sleeps even more than new-born infants usually do; its voice is
very feeble, and rather a whimper than a cry. In the cry of the healthy
infant you at once detect two parts--the