498 BACTERIOLOGY, 



infect. Rabbits, guinea-pigs, white mice, gray house- 

 mice, sheep, and cattle are susceptible. Infection may 

 occur either through the circulation, through the air- 

 passages, through the alimentary tract, or, as we have 

 just seen, through the subcutaneous tissues. 



PROTECTIVE INOCULATION. 



The most noteworthy application of artificially pre- 

 pared living vaccines to the protection of animals 

 from infection is seen in connection with anthrax in 

 sheep and in bovines. 



By a variety of procedures the virulent anthrax 

 bacterium may be in part or totally robbed of its patho- 

 genic properties. It is through the very mild consti- 

 tutional disturbance caused in animals vaccinated with 

 such weakened cultures that protection is often afforded 

 against the severer, frequently fatal, form of the infec- 

 tion. 



Without reviewing the various methods that have 

 been employed for attenuating the virulence of this 

 organism to a degree suitable for protective vaccina- 

 tion, it will suffice to say that the most satisfactory 

 results have been obtained by long-continued cultiva- 

 tion (ten to thirty days) at a temperature of from 42 

 to 43 C. In this procedure the spore-free, virulent 

 bacterium anthracis, obtained directly from the blood of 

 a recently dead animal, is brought at once into sterile 

 nutrient bouillon in about twenty test-tubes, which are 

 immediately placed in an incubator that is carefully 

 regulated to maintain a temperature of 42.5 (T. There 

 should not be a fluctuation of over 0.1 C. 



After about a week a tube is removed from the incu- 

 bator on each successive day and its virulence tested at 



