Protective vaccinations 477 



Marx finds that this method gives results which are much more 

 constant and exact than any other ; this opinion is confirmed at 



Iochst, the largest factory of serums in Germany. 

 VIIT. Vaccinations agai^ist bovine pleuropneumonia. This in- 

 ctive disease is one of the most dreaded scourges of bovine animals. 

 Very contagious, it has spread from central Europe not only into all 

 the other countries of the European continent, but into Africa, 

 America, and almost every quarter of the globe. The virus of this 

 disease was discovered in the serous exudation of hepatised lungs 

 long before the microbiological period of the Medical Sciences had 

 begun. 



Dr Willems of Harselt, who made an experimental investigation, 

 remarkable for the time at which it was carried out (more than half a 

 century ago), demonstrated at once the great virulence of the pul- 

 monary serous fluid ; he found also that the efi*ects of the inoculation 

 of the virus varied much according to the seat of inoculation. When [500] 

 made into the trunk, the neck, or the shoulders, the inoculations are 

 usually fatal ; at the periphery, the lower part of the limbs, at the 

 extremity of the ears or of the tail, the inoculation ordinarily pro- 

 duces merely an inflammatory tumefaction of small extent, which is 

 absorbed in ar few weeks ; after this the animal is refractory to the 

 natural disease. Willems concluded from this that we may vaccinate 

 against pleuropneumonia by inoculating the virulent serous fluid of 

 the lung into the tail. Willems' method of inoculation became a part 

 of current practice 50 years ago. 



For the carrying out of a large number of vaccinations it is 

 necessary to have at one's disposal an adequate quantity of virus ; 

 it was therefore to meet this requirement that researches were first 

 carried out. The serous fluid was withdrawn from the hepatised 

 lungs of animals that had succumbed to the disease and was inocu- 

 lated into normal Bovidae as soon as possible, so as to avoid con- 

 tamination of the fluid. In fact this pulmonary serous fluid often 

 contains foreign germs capable of multiplying rapidly so that it putre- 

 fies very quickly. Pasteur showed that it was possible to remedy 

 these drawbacks by a very simple method by which he could obtain 

 a large quantity of rigorously pure virus. All that is necessary is to 

 inoculate a little of the pleuropneumonic virus below the skin of a 

 weaned calf, behind the shoulder. At the seat of inoculation there 

 is an abundant exudation of virulent serous fluid into the cellular 



