INFECTIOUS DISEASES OF CATTLE. 469 



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

 investigators. The vaccine prepared and distributed by the Bureau 

 of Animal Industry combines the principle of Arloing, Comevin, and 

 Thomas, and the modification of Kitt. 



By vaccination we understand the injection into the system of a 

 minute amount of attenuated — that is, artificially weakened — ^black- 

 leg virus. 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. When 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. 

 This vaccine, which is in the form of a brownish dry powder, is 

 mixed with definite quantities of sterile water, .filtered, and the fil- 

 trate injected by means of a hypodermic syringe under the skin in 

 front of the shoulder of the animal to be vaccinated. The inocula- 

 tion is usually followed by insignificant symptoms. In a few cases 

 there is a slight rise of temperature, and by close observation a 

 minute swelling may be noted at the point of inoculation. The im- 

 munity conferred in this way may last for 18 months, but animals 

 vaccinated before they are 6 months' old and those in badly infected 

 districts should be revaccinated before tlie following blackleg season. 



The efi'ect of the vaccine prepared by this bureau in preventing 

 outbreaks of the disease and in immediately abating outbreaks 

 already in progress has been highly satisfactory, and it is not to 

 be doubted that thousands of young cattle have been saved to the stock 

 owners during the thirteen and a half years in which the vaccine has 

 been distributed. More than IC.OOO.OOO doses have been sent out dur- 

 ing this period, and from reports received it is safe to conclude that 

 more than one-half of this quantity has actually been injected, 

 whereby the percentage of loss from blackleg has been reduced from 

 10, 15, or 20 per cent, which annually occurred before using, to less 

 than 1 per cent per annum. With these figures before us it is plain 

 that the general introduction of preventive vaccination must be of 

 material benefit to the cattle raisers in the infected districts. More- 

 over, there is every reason to believe that with the continued use of 

 blackleg vaccine in all districts where the disease is known to occur 

 and an earnest effort on the part of the stock owners to prevent the 

 reinfection of their pastures by folloAving the directions given, black- 

 leg may be kept in check and gradually eradicated. 



