Protective vaccinations 479 



obtain the pure virus easily, a fact very important in connection with 

 the isolation of the micro-organism. 



Once in possession of pure cultures of the micro-organism of pleuro- 

 pneumonia, Nocard and Roux attempted to make use of it in practical 

 vaccination. They showed that the organism separated by them is 

 capable of producing typical pleuropneumonia when it is inoculated 

 into the appropriate regions of the body of bovine animals. But 

 when inoculated subcutaneously or into the skin of the tail, it 

 produces merely a mild and transient disease which confers an 

 immunity quite as effectual as that set up by the inoculation of the 

 virulent serous fluid. It may be readily understood that, under these 

 conditions, pure cultures may be much more serviceably employed in 

 the practice of vaccination than can Willems' virus from the fact that 

 it is easy to obtain large quantities of absolutely pure cultures. It is 

 easy to predict that the new method will soon replace the old one, 

 very great as are the services the latter has rendered to agriculture. [502] 

 Up to the present, vaccinations with pure cultures have been made in 

 several districts in France with very favourable results. The Pasteur 

 Institute and the Veterinary School at Alfort have already distributed 

 to veterinary surgeons more than 5,000 vaccinal doses of culture ; the 

 protective action of these inoculations has been at least equal to that 

 of the inoculations by Willems' method and the resulting accidents 

 have been reduced hi the proportion of 20 to I 1 . 



The serum of animals hyperimmunised against pleuropneumonia 

 possesses a very distinct protective action, but too little marked and 

 of too short duration to be of any use in practice ; it has also a 

 curative action arresting the invading march of a pleuropneumonic 

 congestion ; but here it is necessary to intervene early, before the 

 appearance of fever, and to inject large quantities of serum. 



The inoculation of a mixture of virus and serum produces no 

 congestion ; but it does not confer any immunity ; the animal remains 

 just as susceptible as the control to the inoculation of the pure virus. 



IX. Vaccinations against typhoid fever. In the preceding 

 sections I have treated more especially of the vaccination of domestic 

 animals against several infective diseases. The information collected 



1 In 1884, in the Department of the Basses- Pyrenees, the Willems' method of 

 inoculation was carried out on 1354 Bovidae ; of this number 10 died and 45 lost 

 their tails completely. In 1901, in the same department, 2800 Bovidae were 

 inoculated with pure cultures, only 1 died and 9 lost their tails. 



