hus causing the serious condition known as blood
poisoning.

[Illustration: FIG. 23.--"THE HISTORY OF A BOIL" (continued). The
migration of leucocytes has continued until now they form a dense mass
surrounding the germs. The poison of the germs has killed all the
leucocytes and also all the cutis immediately around them, and now
digestive fluids from the dead leucocytes is turning the whole dead mass
into liquid pus. The boil has "come to a head." There is a little lump
on the skin and through its thin covering of cuticle can be seen the
yellow pus. (_From Emerson's "Essentials of Medicine."_)]

Inflammation may be treated by means of hot applications, cold
applications, or counter-irritants. The effect of heat is to dilate the
vessels and hence to increase the flow of blood to the injured part.
This increased blood supply makes the reparative process go on more
vigorously, and also makes it possible for the accumulated fluid to be
more rapidly carried away. Moist heat softens the tissues so that pus,
if formed, can escape more easily.

[Illustration: FIG. 24.--"THE HISTORY OF A BOIL" (concluded). The boil
has finally ruptured. The liquid pus has escaped carrying with it the
germs and most of their poisons; the migration of leucocytes has
stopped; the capillaries are returning to normal size and now new tissue
will grow and fill up this hole. (_From Emerson's "Essentials of
Medicine."_)]

Cold acts in just the opposite way. It decreases the size of the blood
vessels so that less blood comes to cause pain and swelling; at the same
time it diminishes the number of white blood corpuscles and the
nutritive substance brought by the blood. The nature and location of the
infection determine whether heat or cold is to be preferred.

Counter-irritants, of which mustard is an example, have a complicated
action. A counter-irritant affects the blood circulation of the place to
which it is applied, and at the same time it irritates the superficial
nerves, which in turn stimulate other more distant nerves. The latter
nerves control the circulation in tissues not adjoining those to which
the counter-irritant is applied, and thus it is possible for a mustard
paste, for example, if applied at one point to bring about changes in
the blood supply of another part of the body. The mechanism by which
counter-irritation is brought about is an intricate nervous process
called reflex action.

HOT APPLICATIONS

In applying either mois