BLACKLEG. 463 



vaccination which has been thoroughlj- tried and proved to be 

 efficacious. 



Prevention. — The various means suggested under "Anthrax" to 

 prevent the spread or recurrence of this disease are equally applicable 

 to blackleg, and hence do not need to be repeated here in full. They 

 consist in the removal of well animals from the infected pasture to a 

 noninfected field, the draining of the swampy ground, the burial or 

 burning of the carcasses to prevent the dissemination of the germs 

 over vast areas through the agency of dogs, wolves, buzzards, or 

 crows, the disinfection of the stables and the ground where the ani- 

 mals lay at the time of death, and, if possible, the destruction of the 

 germs on the infected pastures. One of the most effective methods 

 for freeing an infected pasture from blackleg is to allow the grass 

 to grow high, and when sufficiently dry to bum it off. One burn- 

 ing off is not sufficient to redeem an infected pasture, but the process 

 should be repeated several years in succession. This method, how- 

 ever, is in many instances impracticable, as few cattle owners can 

 afford to do it, and the only means left for the protection of the 

 animals is vaccination. 



iTiimunizatioTh hy vaccination. — Three French veterinarians, Arlo- 

 ing, Cornevin, and Thomas, were the first to discover that cattle may 

 be protected against blackleg by inoculation with virulent material 

 obtained from animals which have died of this disease. Later they 

 devised a method of inoculation with the attenuated or weakened 

 blackleg spores which produced immunity from natural or artificial 

 inoculation of virulent blackleg germs. Their method has undergone 

 various modifications both in regard to the manufacture of the vac- 

 cine and in the mode of its application. Kitt, a German scientist, 

 modified the method so that but one inoculation of the vaccine was 

 required instead of two, as was the case with that made by the French 

 investigators. The vaccine formerly prepared and distributed by 

 the Bureau of Animal Industry combined the principle of Arloing, 

 Cornevin, and Thomas, and the modification of Kitt. 



By vaccination we understand the injection of a minute amount of 

 attenuated — that is, artificially weakened — blackleg virus into the 

 system. This virus is obtained from animals which have died from 

 blackleg, by securing the affected muscles, cutting them into strips, 

 and drying them in the air. ^¥hen they are perfectly dry they 

 are pulverized and mixed with water to form a paste, smeared in a 

 thin layer on flat dishes, placed in an oven, and heated for six hours 

 at a temperature close to that of boiling water. The paste is then 

 transformed into a hard crust, which is pulverized and sifted and 

 distributed in packages containing either 10 or 25 doses. This con- 

 stitutes the vaccine, the strength of which is thoroughly tested on 

 experiment animals before it is distributed among the cattle owners. 



