Transformation, etc., of Pathogenic Microbes. 91 



like themselves. Of two vaccines prepared iu tins 

 way, the iirst comes from heating at 84° during one 

 hour, the second from heating at 82° during the same 

 time. 



The natural serositj of the specific lesions of symp- 

 tomatic charbon may also be attenuated to different 

 degrees by a temperature of 65° to 70°, maintained 

 for a greater or less period of time (Arloing, Corne- 

 vin and Thomas). However, these authors work in 

 preference with serosity dried at a temperature of 30° 

 to 35° ; the dried virus is, in fact, more fixed than the 

 fluid serosity ; it can be preserved indefinitely with its 

 normal virulence; its attenuation requires tempera- 

 tures varying between 60° and 110°. The authors 

 have prepared two vaccines from it: one heated at 

 100°, the other at 85°: Kitt has recommended a sinsrle 

 vaccine heated at 90°. 



4. Attenuation by solar light. — Light is a powerful 

 bactericidal agent ; by the careful use of this prop- 

 erty M. Arloing has succeeded in gradually attenua- 

 ting the charbon bacillus. 



" Thus, a culture exposed to the rays of the sun 

 during nineteen hours furnishes a virus which kills 

 the guinea pig in the dose of one drop ; exposed dur- 

 ing twenty hours, a culture only kills one guinea pig 

 out of two ; exposed during twenty-five hours, such 

 a culture no more kills guinea pigs but vaccinates 

 them, the vegetating power of the bacillus being also 

 considerably diminished." 



The diminution of virulence thus obtained is tem- 

 porary and is not transmitted to later generations of 

 the bacilli. 



5. Desiccation. — Desiccation has been utilized by M. 



