of it during the year
1897. Death rates from diphtheria and typhoid fever have been greatly
reduced by the use of antitoxin and antityphoid vaccine. Thus in New
York State in 1894, before antitoxin was generally used, 99 out of every
100,000 of the population died of diphtheria, while only 20 out of
100,000 died of it in 1914. In 1911 a United States Army Division of
more than 12,000 men camped at San Antonio, Texas, for four months. All
of these men were vaccinated against typhoid fever and only a single
case occurred during the summer, although conditions of camp life always
tend to spread the disease.

While many and various factors tend to lower resistance rather than to
increase it, the idea that these factors act equally in all kinds of
infection is erroneous.

"The principal causes which diminish resistance to
infection are: wet and cold, fatigue, insufficient or
unsuitable food, vitiated atmosphere, insufficient sleep
and rest, worry, and excesses of all kinds. The mechanism
by which these varying conditions lower our immunity must
receive our attention, for they are of the greatest
importance in preventive medicine. It is a matter of common
observation that exposure to wet and cold or sudden changes
of temperature, overwork, worry, stale air, poor food,
etc., make us more liable to contract certain diseases. The
tuberculosis propaganda that has been spread broadcast with
such energy and good effect has taught the value of fresh
air and sunshine, good food, and rest in increasing our
resistance to this infection.

"There is, however, a wrong impression abroad that because
a lowering of the general vitality favors certain diseases,
such as tuberculosis, common colds, pneumonia, septic and
other infections, it plays a similar role in all
communicable diseases. Many infections, such as smallpox,
measles, yellow fever, tetanus, whooping-cough, typhoid
fever, cholera, plague, scarlet fever, and other diseases,
have no particular relation whatever to bodily vigor. These
diseases often strike down the young and vigorous in the
prime of life. The most robust will succumb quickly to
tuberculosis if he receives a sufficient dose of the
virulent micro-organisms. A good physical condition does
not always temper the virulence of the disease; on the
cont