INTRODUCTION 1$ 



be other substances in the blood which caused the 

 disease. 



In the late seventies Pasteur and his pupils reproduced 

 anthrax in animals from a pure culture of anthrax 

 bacilli grown outside the body of an animal, thus con- 

 firming Davaine's observations and settling the question 

 of the cause of anthrax. Koch, in 1882, discovered the 

 tubercle bacillus and proved it to be the cause of tuber- 

 culosis. 



Jenner, a hundred years before, had produced im- 

 munity to small-pox by inoculating with a modified 

 form of the disease cow-pox; and Pasteur, now working 

 along similar lines, produced immunity to anthrax by 

 inoculating animals with a culture of the germ which had 

 been attenuated by heating. Behring, in 1893, P ro " 

 duced diphtheria antitoxin, and the beginning of the end 

 of the conflict of the ages was apparent. Flexner has 

 produced a curative serum of great value in cerebro- 

 spinal meningitis, and vaccination against typhoid fever 

 is proving very valuable in the armies of the world. 

 In view of the progress made in the establishment of im- 

 munity in the last twenty-five years, it is not too much 

 to expect that the middle of the twentieth century will 

 see the production of immunizing agents for practically 

 all infectious diseases. 



