XXXVlii INTRODUCTION. 



may occur while his main position remains impreg- 

 nable. Such a result, for example, as that obtained 

 in presence of so many witnesses at Melun must 

 surely remain an ever-memorable conquest of science. 

 Having prepared his attenuated virus, and proved, by 

 laboratory experiments, its efficacy as a protective 

 vaccine, Pasteur accepted an invitation from the 

 President of the Society of Agriculture at Melun, to 

 make a public experiment on what might be called an 

 agricultural scale. This act of Pasteur's is, perhaps, 

 the boldest thing recorded in this book. It naturally 

 caused anxiety among his colleagues of the Academy, 

 who feared that he had been rash in closing with the 

 proposal of the President. 



But the experiment was made. A flock of sheep 

 was divided into two groups, the members of one group 

 being all vaccinated with the attenuated virus, while 

 those of the other group were left unvaccinated. A 

 number of cows were also subjected to a precisely 

 similar treatment. Fourteen days afterwards, all the 

 sheep and all the cows, vaccinated and unvaccinated, 

 were inoculated with a very virulent virus ; and three 

 days subsequently more than two hundred persons 

 assembled to witness the result. The ' shout of 

 admiration,' mentioned by M. Eadot, was a natural 

 outburst under the circumstances. Of twenty-five 

 sheep which had not been protected by vaccination, 

 twenty-one were already dead, and the remaining ones 



