752 GENEEAL THEEAPEUTIC MEASUEES 



theory consists in the fact that, by modifying the virulence 

 or action of the bacteria in some way, there are produced in 

 the inoculated animal antitoxins. These not only prevent the 

 occurrence of the- inoculated disease, but even the develop- 

 ment of the disease when introduced by natural channels. 

 The activity of bacteria is lessened in various ways. Thus 

 in preparing the vaccines against anthrax and blackleg the 

 bacteria are exposed to heat. Then by inoculating the 

 bacteria in a way, different from that in which they naturally 

 gain entrance to the body, their activity may be diminished; 

 e.g., the bacillus of blackleg is introduced under the skin or 

 intravenously, and the tail is sometimes chosen as a site, the 

 blood supply being poor. The vaccines blackleg and anthrax 

 do not prove curative if employed after the development of 

 the disease, against which thev are preventives, and often ■ 

 they are ineffectual if used after the exposure of the animal 

 to the infection of the disease. This is not the case in anti- 

 rabic inoculation, however, as the treatment proves success- 

 ful after the patient has been bitten and infected by a rabid 

 animal. So in smallpox in the human, vaccination will 

 modify and possibly prevent smallpox if done within four 

 days after exposure to infection. The duration of the period 

 of immunity conferred by vaccination differs in the case of 

 the different vaccines. 



Blackleg or Quarter Evil. — This disease is caused by 

 B. Chauvoei and is distinct from anthrax. Calves should be 

 vaccinated when six months old and again within a year. 

 The best time is that before the usual occurrence of the 

 disease, and no surgery, as branding, castration, marking, 

 dehorning or spaying, should be done before, or within two 

 weeks after, vaccination. Either one or two vaccines 

 are used, the first being the weakest and prepared by heat- 

 ing to 103° C, and the second being heated to 93° C. and 

 used eight days later. Vaccination is done with a powder 

 obtained by drying and triturating a piece of affected muscle. 

 The Chief of the Bureau of Animal Industry, U. S. Agri- 

 cult. Dep't., Washington, D. C, supplies gratis to stock own- 

 ers black leg vaccine and directions for using the same. One 

 dose given subcutaneously is usually sufficient to protect the 

 animal for life against black leg, if used after the animal is 



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