478 Chapter XV 



tissue, from which we are enabled to collect large quantities of 

 pure virus. 



In some countries, as in Germany and in Australia, institutions 

 have been founded for the production by this method of the virulent 

 serous fluid necessary for these inoculations. 



The virus should be inoculated into the tip of the tail of animals 

 that it is desired to immunise, because the temperature in this situa- 

 tion is relatively low and the connective tissue is dense and not very 

 abundant. The inoculation is made with a lancet or a Pravaz syringe. 

 The vaccination is generally borne well, in spite of the reaction 

 phenomena which are manifested about two weeks after the intro- 

 duction of the virus. At that time a febrile condition is set up and 

 a swelling manifests itself at the point of inoculation, which, however, 

 soon retrogresses and then disappears. 



The immunity conferred by Willems' method is substantial and 

 lasting (for one or two years and even longer) ; this explains its great 

 success in the hands of breeders and veterinarians. Accidents fol- 

 [501] lowing its use are rare, and the mortality does not exceed 1 per cent. 



In spite of all these advantages a new method was still desirable, 

 a method which would allow of the preparation of large quantities 

 of virus of a suitable and uniform activity under conditions of irre- 

 proachable purity. Thanks to the discovery of the micro-organism 

 of pleuropneumonia which we owe to Nocard and Roux^ this object 

 has been achieved. With the collaboration of Borrel, Salimbeni, and 

 Dujardin-Beaumetz, they succeeded in demonstrating and isolating 

 this micro-organism, the smallest of all known living organisms. The 

 first steps in these researches were very laborious, but later the 

 organism of pleuropneumonia was cultivated on fluid and solid media: 

 Martin's broth (prepared with pigs' stomachs) or agar with the 

 addition of a certain quantity (about S^o) of fresh ox serum. The 

 serum-broth, sown with pure pneumonic serous fluid, gives only a 

 moderate growth, which becomes only slightly turbid and contains 

 micro-organisms so small that it is impossible to distinguish them 

 individually. They can be made out only when massed together in 

 irregular clumps. The minuteness of this micro-organism is evidenced 

 by the ease with which it passes through a Berkefeld filter, and even 

 through certain Chamberland candles (F). This feature enables us to 



^ Ann. de VInst. Pasteur, Paris, 1898, t. xii, p. 240 ; Cinquanten. d. I. Soc. d. 

 hiol., Paris, 1899, p. 440; Dujardin-Beaumetz, "Le microbe de la p^ripueumonie,'* 

 These de Paris, 1900. 



