578 PATHOGENIC BACTERIA. 



Milk also seems to be a favorable culture-medium. 

 The development of the bacilli is unaccompanied by 

 coagulation. 



The virulence of the organism is soon lost in all 

 culture-media, but it is said that the virulence of the 

 culture can be much increased by the addition to it of 

 20 per cent, of lactic acid. 



When susceptible animals are inoculated with a minute 

 portion of a pure culture in a little subcutaneous pocket, 

 such as is described in connection with tetanus and 

 malignant edema, the bacilli proceed to grow, pro- 

 duce the well-known affection, and lead to a certainly 

 fatal outcome. Cows seem to be the most susceptible 

 animals, especially those between six mouths and four 

 years old ; sheep and goats are also sometimes affected. 

 Curiously enough, animals that are immune to malig- 

 nant edema are seemingly more susceptible to Rausch- 

 brand. Of the laboratory animals, the guinea-pig is 

 most susceptible ; swine, dogs, and rabbits are very 

 slightly susceptible ; horses, goats, and birds are im- 

 mune. 



The virulence of the bacillus is capable of ready 

 attenuation by exposure to heat, by previous exposure 

 of its spores to heat, or by drying combined with ex- 

 posure to increased temperature. The inoculation of 

 animals with the attenuated bacilli causes a very mild 

 affection, followed by complete immunity to the viru- 

 lent organisms. Upon this principle the "protective 

 vaccination" is based. Kitt has shown that dried mus- 

 cle from an infected animal is more efficacious for the 

 purpose of immunizing than the cultures themselves. 

 The method for preparing these so-called " vaccines" is 

 very simple. A calf is inoculated with a virulent culture 

 in the most muscular parts of its body. As soon as it 

 dies the "black spongy muscular tissue is dissected out, 

 cut in small pieces, and dried in an oven at about the 

 body-temperature. When dry the muscle is firmly 

 ground, then heated for the purpose of attenuating the 



