a suitable interval, he is again injected with
diphtheritic poison, and for the second time his blood begins to
generate the antitoxine. And the process is repeated again and again,
the virulence of the poison being increased each time, until the horse's
blood is fairly reeking with antitoxine. Then blood is drawn freely from
the horse, and it is allowed to separate into clot and serum, the
latter alone being the part destined for use. This serum is tested on a
small animal that has been inoculated with a deadly dose of the
diphtheritic poison; if it saves the little creature from death, it is
assumed to be potent enough for use on human beings, and, handled with
all possible precautions against putrefaction or any contamination with
pathogenic bacteria, it is furnished to physicians, its degree of
potency being designated in "units."

If in this brief article, which does not purport to be more than a
sketch of the tremendous strides made by medicine in the Nineteenth
Century, so much space has been given to the germ theory of disease, it
is because the demonstration of the truth of that theory has been
absolute, and has constituted the very marrow of almost all the medical
progress of the century that has been the outcome of continuous thought
and study as opposed to chance discovery.

Such results as the germ theory has now led to in the treatment of
diphtheria it had already accomplished in the field of surgery as a
consequence of that strict asepticism which, originating with Joseph
Lister (now Lord Lister), and rapidly carried by him to a condition
verging on technical completeness, was soon taken up by surgeons all
over the world and brought wellnigh to perfection, so that the mortality
of wounds of all sorts has been tremendously reduced, and many surgical
operations are now practised frequently--indeed, whenever the occasion
for them arises--that before the days of Listerism would have been
looked upon as almost tantamount to the patient's death-warrant. More
particularly is this the case as to operations which involve opening
into the abdomen, the chest, or the cranium. So little risk now attaches
to such operations, properly performed, that the opening of the
abdominal cavity for the mere purpose of ascertaining the condition of
its contents--"exploratory laparotomy," as it is called--is a matter of
constant occurrence. Curiously enough, in some way not yet
satisfactorily explained, that procedure in itself,