308 Manual of Veterinary Microbiology. 



In order to obtain a regular and stable attenuation 

 Pasteur starts with the cord of a rabbit which has 

 been rendered rabid by means of fixed virus ; he di- 

 vides it into segments of two centimeters in length 

 and these he suspends in a wide-mouthed liter bot- 

 tle containing pieces of caustic potash ; this bottle 

 is placed in a chamber in which the temperature is 

 maintained at 20° C. 



Variations in the temperature lead to modifications 

 in the attenuation ; at 28° the virulence is destroyed 

 in five days ; at 35° in four hours. 



The Russian rabbit, which has a smaller cord, al- 

 lows of a more rapid attenuation. 



The temperature and the oxygen of the air are 

 instrumental in producing this loss of pathogenic 

 activity; the attenuation is slower in carbonic acid; 

 the loss of humidity seems to have less influence ; 

 ProtopopofF has, indeed, shown that this modication 

 occurs also in glycerin-bouillon. 



Authorities are far from being unanimous as to 

 the theory of this attenuation. Pasteur thinks that 

 it consists merely in an impoverishment in active 

 virus and not in a diminution of activity. 



The hypothesis of a chemical vaccine has been dis- 

 pelled by Babes who showed that the rabic sub- 

 stance filtered through porcelain, as ^vell as that 

 heated to 100°, has no vaccinal property. Gamaleia 

 has demonstrated that vaccinal injections have no 

 action on an individual already afiected with the dis- 

 ease, whicii also dispels the theory of a chemical vac- 

 cine. Virus attenuated by desiccation regains the 

 activity of the fixed virus on its second passage 

 through the rabbit. 



