VACCINATION 145 



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 germs 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 



