INFECTIOUS DISEASES 01? CATTLE. 451 



of Animal Industry combines the principle of Arloing, Cornevin, 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 — blackleg 

 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 trans- 

 formed into a hard crust, which is pulverized and sifted and distrib- 

 uted in packages containing either 10 or 25 doses. This constitutes 

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

 animals before it is distributed among the cattle owners. This vac- 

 cine, which is in the form of a brownish dry powder, is mixed with 

 definite quantities of sterile water, filtered, and the filtrate injected by 

 means of a hypodermic syringe under the skin in front of the shoul- 

 der of the animal to be vaccinated. The inoculation is usually fol- 

 lowed 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 immunity conferred in 

 this way may last for eighteen months, but animals vaccinated before 

 they are 6 months old and those in badly infected districts should be 

 revaccinated before the following blackleg season. 



The effect 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 six and a half years in which the vaccine has been dis- 

 tributed. More than 7,700,000 doses have been sent out during 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 per- 

 centage 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. Moreover, 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 following the directions given, blackleg may be kept in 

 check and gradually eradicated. 



NECROTIC STOMATITIS (CALF DIPHTHERIA). 



Necrotic stomatitis is an acute, specific, highly contagious inflam- 

 mation of the mouth, occurring in young cattle and characterized, 



