tina, or the eruption on the skin in smallpox, and their course is
more or less strictly limited by distinct periods of increase, acme, and
decline. No such rule obtains in the case of consumption, scrofula, and
rickets, which are instances of chronic constitutional diseases. In them
too the local manifestations of the general disease vary also: the lungs
being affected in one case of consumption, the bowels in another; while
scrofula may show itself by affection of the glands in one case, by the
formation of abscesses in a second, or by disease of the bones in a
third.

=Chronic Constitutional Diseases.=--It may perhaps be convenient to
study first the chronic constitutional diseases; and afterwards to make
a few, and they will be but few, remarks on fevers.

=Consumption= and Scrofula, though similar, are not the same disease.
Both, however, depend on some defect in the blood, as the result of
which certain materials, incapable of being converted into the natural
constituents of the body, are deposited in the substance of different
external parts or internal organs. If deposited in small quantities,
these materials may be absorbed, as it is termed, that is to say, got
rid of, by natural processes, which even now we understand but
imperfectly.

If deposited more abundantly, they press upon and gradually spoil the
healthy parts in which they are seated, and thereby interfere with the
proper performance of their duties. Thus, the deposit of consumption
encroaches on the proper substance of the lungs, and so lessens the area
in which the blood is exposed to the air and purified: the deposit of
scrofula around and in a joint interferes with its powers of movement.
Nor is this all; but wherever any deposit has once taken place, it tends
especially to increase in that very spot, guided as it were by a certain
affinity; and the substance of the previously healthy part is removed as
fresh deposit comes to occupy its place. Further, the matter deposited
has no power of being changed into healthy substance of lung, or of
bone, or of any other part.

A fractured limb may be completely mended; a fluid is poured out around
and between the edges of the broken bone; by degrees this hardens, it
undergoes changes which convert it into solid bone, and the limb is once
more as serviceable as before, though some indications of the fracture
may still be perceptible in the texture of the bone itself. Or, a person
receives a severe blow