310 RABIES 



by dr^-ing and b^- the action of light. In dry air, protected 

 from light and putrefaction, the virulence of the spinal cord of 

 rabbits is destroyed in fourteen to fifteen da}'s. When spread 

 in thin layers it is entirely destroyed by drying in from four to 

 five da3^s. Sunlight destroys it in about fortj' hours. The 

 loss of virulence by drying is gradual but quite regular, which 

 fact was taken advantage of by Pasteur in the preparation of his 

 vaccine. The virus may be preserved in neutral glycerin at 

 ordinary temperature for a long time. Roux found that after 

 four weeks in glycerin at 30° C, the virus in a rabid brain 

 had the same power as when perfectly fresh. The writer has 

 lound that rabbits inoculated with rabid brains that had been 

 kept in glycerin from three to four weeks did not develop the 

 disease as quickly as when they were inoculated with the 

 freshly removed brain. 



It is quite resistant to putrefaction. Galtier has found 

 the virus active in the central nervous system of rabbits buried 

 for twenty-three days, of sheep buried thirtj'-one days and of 

 dogs buried forty-four days. Other observers have found it 

 still active in animals buried for twenty-four days. 



It is destroj'ed completely b}- a temperature of 50° C. in 

 one hour or 60° C. in one-half hour. It is uninjured by 

 exposure to extreme cold, resisting the prolonged application 

 of a temperature from 10 to 20° C. below zero. 



Its activit}- is destroyed in one hour by a five per cent 

 solution of carbolic acid, or by a i to 1,000 solution of corro- 

 sive sublimate. Water saturated with iodine destroyes it in 

 ten minutes. 



;^ 239. Period of incubation. The period of incuba- 

 tion is quite variable depending on the site of the wound 

 which is almost always a bite, the amount of virus introduced 

 and its virulence. In general it may be said for all animals 

 that the period of incubation seldom exceeds sixty days, 

 though in man and in some of the larger animals, it some- 

 times, though very rarely reaches one year. A few cases of a 

 longer period have been reported. The average period as 

 given by Ravenel is as follows : 



In man, 40 days. 



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