PERIOD OF INCUBATION 467 



It is quite resistant to putrefaction. Galtier found the 

 virus active in the central nervous system of rabbits that had 

 been buried for twenty-three days, of sheep buried thirty-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 destroyed completely by a temperature of 50° C. in 

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

 posure to extreme cold, resisting the prolonged application of 

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



Its activity 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 destroys it in 

 ten minutes. 



§ 371. 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, al- 

 though in man and in some larger animals, it sometimes, 

 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. 



In dogs, 21 to 40 days. 



In horses, 28 to 56 days. 



In cats, 14 to 28 days. 



In pigs, 14 to 21 days. 



In goats and sheep, 21 to 28 days. 



In birds, 14 to 40 days. 



In rabbits inoculated subdurally with the brain from rabid 

 animals, the writer has found the period of incubation to vary 

 from 12 to 62 days and the duration of the disease to range 

 from a few hours to three days. Westbrook reports a period 

 of incubation in rabbits to extend in one case over a hundred 

 days. In the disease as it is naturally contracted from the 

 bites of rabid animals, the period of incubation varies with 



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