VACCINATION 
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risks of the disease. Some bacteria seem to produce 
their harmful effects not so much by the poisons which 
they set free as by something stored up in the bodies 
of the getrns themselves. But if the living germs 
are put into the body, they may cause the disease, and 
the very thing to be guarded against might thus be 
precipitated. 
So the attempt was made to avoid this risk by kill¬ 
ing the germs by heat and then injecting these dead 
organisms beneath the skin of the person to be pro¬ 
tected. This method has been practiced on a large 
scale in some countries with the typhoid fever bacillus 
and with the bacillus of the plague. While some meas¬ 
ure of protection seems to have been secured in this 
way, the method has not been very generally adopted. 
There are two other forms of artificially induced 
immunity which we must consider briefly, since they 
belong among the greatest life-saving agencies at our 
command today. I refer to vaccination for protection 
against smallpox and the preventive inoculations for 
rabies or hydrophobia. 
VACCINATION 
First, vaccination to prevent smallpox. If the good 
Dr. Jenner, who more than a hundred years ago did 
some excellent observing and some clear thinking 
about what he saw, and found out how to prevent 
smallpox, could listen to our up-to-date talk about bac¬ 
teria, microbes, toxins and antitoxins, and various 
phases of immunity, he would not understand a word 
