S66 MICROBIOLOGY OF SPECIAL INDUSTRIES 



with the vaccine under test; three each with, three-fourths the dose for 

 cattle, three each with one-half dose and the remaining two with one- 

 third dose. 



Temperatures of the test animals should be recorded for three sub- 

 sequent days. Vaccine of proper strength is indicated when thermal 

 reactions occur in practically all the test animals together with local 

 reactions in some instances. None of the animals in the series should 

 die. 



As an additional test for potency a heifer may be injected sub- 

 cutaneously with one dose and a few weeks after the vaccination the 

 animal may be exposed to the disease by receiving an injection of the 

 virulent living organisms. If the animal remains normal the activity 

 of the product is indicated. In order to test the vaccine in regard to 

 safety, heifers may be injected with several doses each. The absence of 

 severe disturbances shows that the material may be used without 

 danger. 



For the purpose of eliminating possible danger from the use of 

 blackleg vaccine a "double vaccine" may be employed. This consists 

 of two vaccines, each possessing different degrees of attentuation, which 

 are controUied by the degree of heat and the period of time used m attenu- 

 ating the organisms in the affected muscle tissue. When the final 

 product, either single or double blackleg vaccine, is ready for use it is 

 usually distributed in the form of a powder, prepared threads or small 

 pills. The latter, first suggested by Houghton in 1898, are injected 

 hypodermically. 



Rabies Vaccine. — The successful preventive treatment for rabies, 

 or hydrophobia resulted from the brilliant researches of Pasteur. 

 The method devised by Pasteur in 1885, with some modifications, con- 

 tinues to be the only practical, specific preventive treatment for rabies. 

 This treatment consists of a series of vaccinations, each vaccination 

 involving the apphcation of rabies virus having a known degree of 

 attentuation. In each succeeding application of modified' rabies virus 

 the patient receives increasingly more virulent material until finally 

 active immunity is acquired and subsequent attack from the disease 

 is successfully resisted. 



The preparation of rabies vaccine begins with the attenuation of a 

 virus having a known degree of virulence. The material may be secured 

 from an ordinary case of "street rabies." A dog suffering from the 



