I must refer you on this subject again to Andrew Combe's
"Physiology," especially chapters iv. and vii.; and also to
chapter x. of Madame de Wahl's excellent book. I will only say
this shortly, that the three most common causes of ill-filled
lungs, in children and in young ladies, are stillness, silence,
and stays.

First, stillness; a sedentary life, and want of exercise. A girl
is kept for hours sitting on a form writing or reading, to do
which she must lean forward; and if her schoolmistress cruelly
attempts to make her sit upright, and thereby keep the spine in an
attitude for which Nature did not intend it, she is thereby doing
her best to bring on that disease, so fearfully common in girls'
schools, lateral curvature of the spine. But practically the girl
will stoop forward. And what happens? The lower ribs are pressed
into the body, thereby displacing more or less something inside.
The diaphragm in the meantime, which is the very bellows of the
lungs, remains loose; the lungs are never properly filled or
emptied; and an excess of carbonic acid accumulates at the bottom
of them. What follows? Frequent sighing to get rid of it;
heaviness of head; depression of the whole nervous system under
the influence of the poison of the lungs; and when the poor child
gets up from her weary work, what is the first thing she probably
does? She lifts up her chest, stretches, yawns, and breathes
deeply--Nature's voice, Nature's instinctive cure, which is
probably regarded as ungraceful, as what is called "lolling" is.
As if sitting upright was not an attitude in itself essentially
ungraceful, and such as no artist would care to draw. As if
"lolling," which means putting the body in the attitude of the
most perfect ease compatible with a fully-expanded chest, was not