wn, there need be but little fear in the future of
this old enemy of man again getting control and spreading without
hindrance throughout a whole country.

CHAPTER XX

_DISEASES CONTROLLED BY ANTITOXINS (SMALLPOX, RABIES, TETANUS)_

_Smallpox._

A hundred years ago, the most dreaded disease in this country or in
Europe was smallpox; and even yet writers of fiction, when they desire
to expose their hero to the most harrowing conditions possible, leave
him in a deserted hut with a man dying of smallpox. But to the educated
person of to-day smallpox is encountered absolutely without dread, since
it has been robbed of its terrors by the introduction of vaccination. As
far back as 1717, Lady Mary Montague, writing home to England, described
the eastern method of taking smallpox deliberately, under comparatively
agreeable conditions, in order that severe cases of the disease might be
prevented.

Why one attack of the disease should prevent a subsequent case was not
known, nor why inoculation with other virus than that of the disease
itself should be efficient was not known. But the fact was thoroughly
established then that in some way, in the process of the disease and
recovery, there was left in the body some substance or agency which was
sufficiently powerful to ward off subsequent attacks.

In 1796, Dr. Jenner discovered that a disease very similar to smallpox
existed in the cow, and that if the scab from a pustule on the cow was
used for inoculation instead of similar material from a smallpox
patient, the resulting disease would be less severe and the protection
against subsequent attacks equally efficient. Since that time,
therefore, cowpox matter or vaccine has been used to develop a mild form
of disease for the express purpose of preventing subsequent attacks.

This is the fundamental principle involved in all antitoxin treatment,
and the only difference between vaccination and the injection of
diphtheria antitoxin is that with vaccination the disease and the
consequent protection is developed in the individual during the course
of the disease, while with diphtheria the first attack of the disease
and the resulting protective agencies are developed first in the horse
and then the essential elements of the blood are introduced into the
patient, thereby increasing his resistance to the disease. Smallpox, of
all diseases, formerly claimed the largest number of deaths. A hundred
years ago, persons marked wi