their causing a dilatation of the vessels, and so inducing a hyperæmia
in the affected area. It has been shown experimentally that repeated,
short applications of moist heat (not exceeding 106° F.) are more
efficacious than continuous application. It is now believed that the
so-called _counter-irritants_--mustard, iodine, cantharides, actual
cautery--act in the same way; and the method of treating erysipelas by
applying a strong solution of iodine around the affected area is based
on the same principle.

[Illustration: FIG. 6.--Passive Hyperæmia of Hand and Forearm induced by
Bier's Bandage.]

While these and similar methods have long been employed in the treatment
of inflammatory conditions, it is only within comparatively recent years
that their mode of action has been properly understood, and to August
Bier belongs the credit of having put the treatment of inflammation on a
scientific and rational basis. Recognising the "beneficent intention" of
the inflammatory reaction, and the protective action of the leucocytosis
which accompanies the hyperæmic stages of the process, Bier was led to
study the effects of increasing the hyperæmia by artificial means. As a
result of his observations, he has formulated a method of treatment
which consists in inducing an artificial hyperæmia in the inflamed area,
either by obstructing the venous return from the part (_passive
hyperæmia_), or by stimulating the arterial flow through it (_active
hyperæmia_).

_Bier's Constricting Bandage._--To induce a _passive hyperæmia_ in a
limb, an elastic bandage is applied some distance above the inflamed
area sufficiently tightly to obstruct the venous return from the distal
parts without arresting in any way the inflow of arterial blood (Fig. 6).