2o6 MANUAL OF BACTERIOLOGY. 



hour with i loo revolutions a minute, using the virus diluted i 

 to 50 and I to 100 deprives the virus of its virulence. He also 

 found that the virus traveled along the nerves and not the 

 lymphatics in the rare cases of successful inoculation of ani- 

 mals into a pathologically hypertrophied ganglion.* 



Tizzoni and Bongiovannif found that radium rays not only 

 destroy the virulence of rabies virus in vitro, but also counter- 

 act the effects of the virus in animals inoculated and exposed to 

 the rays, and furthermore the rays transform the virus into 

 an excellent antirabic virus. Still more remarkable is their 

 statement that radium rays cure the disease after symptoms 

 have developed. 



Pasteur discovered that rabies could be produced in animals 

 by inoculation under the dura mater with portions of the spinal 

 cord of a dog suffering from hydrophobia. He also found that 

 successive passages through a series of rabbits greatly increase 

 the virulence of the virus, as indicated by a much shorter period 

 of incubation after inoculation. The first rabbit of the series 

 inoculated with the "street" rabies virus — i. e., from a spon- 

 taneous case in a dog — dies in about two weeks, and each 

 succeeding rabbit dies in a shorter and shorter time until 

 ultimately the incubation period is reduced to six or seven' days. 

 Beyond this the strength of the virus cannot be increased, and 

 is called "virus fixe," or the fixed virus. Pasteur found, more- 

 over, that the cord of the rabbit which has attained this degree 

 of virulence is attenuated by various agencies, notably by dry- 

 ing, and that animals injected with this attenuated virus can 

 withstand inoculations of more potent virus. By drying for 

 various lengths of time a series of "vaccines" of exactly graded 

 potency is obtained, and starting with the vaccine of least po- 

 tency an animal can be inoculated with increasingly potent virus 

 until it will withstand inoculations of the virus fixe itself. 



*Bull. de I'Inst. Past. Vol. IV., 1906 p. 448. 



tAcad. d. sciences de Bologne. Avril, 1905. p. 6. Abst. Bill, de I'Inst. 

 Pasteur. T. III., No. 13. 15 Juillet, 1905. p. 582. 



