210 DISCOVERY CH. 



of cattle and sheep died annually from the disease. A 

 formidable yearly tribute had to be paid to this 

 mysterious scourge until enlightenment came through 

 the labours of Robert Koch and Louis Pasteur. 



Koch cultivated a microbe from the blood of an 

 animal that died from anthrax, and he found that when 

 this microbe was inoculated into guinea-pigs, rabbits 

 and mice, they inevitably took the disease. Pasteur 

 proved that the power of conveying anthrax was due 

 to the bacillus, and to it alone ; and, later, he suggested 

 that, by vaccination of animals with the virus, it would 

 be possible to give them the disease in a mild form, and 

 so secure their immunity from fatal attacks. His 

 conclusions met with the usual reception of ridicule 

 from the practical man concerned with the care of 

 cattle ; and the veterinary profession proposed an 

 experiment to test them. Pasteur accepted the chal- 

 lenge, and the conditions of the battle between knowledge 

 and incredulity were drawn up. Sixty sheep were put 

 at his disposal ; twenty-five were vaccinated, by two 

 inoculations, with the attenuated virus of anthrax. 

 Some days later these, and twenty-five others, were 

 inoculated with some very virulent cultures of the 

 anthrax bacillus. Ten sheep underwent no treatment 

 at all. 



" The twenty-five unvaccinated sheep will all perish," 

 wrote Pasteur ; "the twenty-five vaccinated sheep will 

 survive." The result turned out exactly as he had 

 predicted. The sheep which had been vaccinated with 

 a mild form of anthrax, in order to make them more 

 capable of resisting the later inoculation, survived, 

 while those which had not thus been rendered immune, 

 perished. The conclusion of the experiment is one of 

 the most dramatic incidents in the history of science, 



