270 MICROBES AND TOXINS 



ii. Vaccination with Attenuated Cultures. 



Anthrax. The anthrax vaccines are cultures attenuated 

 by contact with the air at a temperature of 42*5 C. Two 

 graduated vaccines are employed : the weaker kills mice and 

 small guinea-pigs, the stronger kills adult guinea-pigs and even 

 a certain percentage of rabbits. The animals treated with 

 these preserve their immunity for about a year, and it has been 

 calculated that during the twenty years which followed their 

 introduction at least twelve million animals were inoculated. 

 The method of anthrax vaccination has never required alter- 

 ation since its discovery by Pasteur, Chamberland, and Roux, 

 and the celebrated experiment of Pouilly-le-Fort. 



Swine-Erysipelas. In this the same principle is 

 employed, /.<?., a virus attenuated in the laboratory. But the 

 bacillus of swine-erysipelas does not produce spores, and a 

 method of sero-vaccination has been invented instead (v. infra). 



Hi. Pleuropneumonia of Cattle (Rinderpest). 



The discovery of the microbe dates only from 1898, but 

 vaccination had been practised against the disease a con- 

 siderable time before. Willems employed as virus the serous 

 fluid from the diseased lungs : he had observed that inoculation 

 of this in a healthy animal produced variable effects according 

 to the site of injection chosen : injected on the trunk or neck 

 the infection was fatal ; at the tip of the tail or of the ears it 

 produced only a limited inflammation which left the animal 

 immune towards the naturally occurring disease. 



The first improvement was introduced by Pasteur, who 

 showed that the pure virus could be got by taking the abundant 

 exudate produced in the subcutaneous tissue of a calf after 

 inoculation there. Later, pure cultures were substituted. 



The tip of the tail is a good site for vaccination, since the 

 tissue is dense and the absorption slow. A few animals lose 

 their tails as a result of the vaccination. 



