516 ANNUAL REPORT OF THE Off. Doc. 



partly to the greater activity of tlie virus as fonud in them, and 

 partly to their mode of attack, wounds about the face and heads 

 being conjmoH. and the wounds being very extensive. 



Of animals bitten by rabid dogs, it is claimed that only from 20 

 to 30 per cent, become infected. Roll calculated that during the 

 years 1877-1887 the percentage in horses was about 40, among cattle 

 and sheep, 50, among pigs, 36, ".nd among goats, 20. It will be 

 seen from these figures how unnecessary it is to destroy all animals 

 bitten by dogs believed to be or even known to be made. 



Period of Incubation. By the period of incubation is meant the 

 time which passes between the introduction of the virus or germ of 

 a disease, and the appearance of the symptoms. This is quite vari- 

 able in rabies, depending on the site of the wound, which is almost 

 always a bite, the amount of virus introduced, and the strength 

 of the virus. In general it may be isaid for all animals that the 

 period of incubation seldom exceeds sixty days, though in man 

 and in some of the larger animals, it sometimes, though very rarely, 

 reaches one year. The average period is as follows: 



In man, 40 days. 



In dogs, 21 to 40 days. 



In horses, 28 to 56 days. 



In cows, 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. 

 Influence of Seasons. It has been for a long time believed, 

 and apparently with fi certain degree of truth, that rabies in dogs is 

 more frequent during the hot months than at other periods of the 

 year, and as a result of this we would expect to find more persons 

 bitten during the periods of extreme heat than during the rest of 

 the year. The old statistics in France, dating from the year 1850 

 to 1876, indicate that 30.4 per cent, of all cases of rabies occurred 

 during the months of June, July and August. The figures col- 

 lected at the Pasteur Institute in I'aris do not, however, agree with 

 these, the maximum number of bitten persons applying for treat- 

 ment there during the years 1886 to 1893 being in :March, April and 

 May, and the minimum number in September, October and November. 

 The statistics collected bv Boulev give for December, Januarv and 

 February, 755 cases; March, April and May, 857 cases; June, July 

 and August, 788 cases, and September, October and November, 696 

 cases, showing a fairly uniform distribution for the whole year. 

 The maximum number, occurring during March, April and May, 

 agrees wlHi llic figures of the Pasteur Institute. 



