THE LABOEAT011Y OF THE ECOLE NORMALS. 285 



After having had recourse to the oxygen of the air to 

 attenuate the virulence of the microbe, Pasteur made 

 some experiments in vaccination. Some pigs which 

 had been vaccinated remained in the canton of Bol- 

 lene, under the supervision of M. Maucuer, the 

 owners having pledged themselves to keep their 

 vaccina.ted pigs for at least a year. In the ensuing 

 September, when swine fever raged everywhere in the 

 canton of Bollene and in the arrondissement of Orange, 

 not a single vaccinated pig was attacked. ' They are all 

 flourishing,' wrote M. Maucuer. An address of thanks 

 was sent to Pasteur by the municipal council of 

 Bollene. 



But, notwithstanding these happy results, the 

 question of the application of vaccines to different 

 breeds requires still further investigation, before the 

 vaccination of pigs can become general. 



Soon afterwards a method, different from that of 

 the atmospheric oxygen, for weakening the virulence of 

 the fever virus, was tried in the laboratory. 



Pasteur had proved that viruses are not morbid 

 entities, that they can assume numerous forms, and 

 especially physiological properties, dependent on the 

 medium in which they live and multiply. The viru- 

 lence belongs to living microscopic species, but is at 

 the same time essentially modifiable. It may be 

 weakened or intensified, and each of these states is 

 capable of being made permanent by culture. A* 



