460 Chapter XV 



improvement can still be made in this branch of practice. If science 

 should succeed some day, as we may be permitted to hope it will, in 

 finding the micro-organism of vaccinia and of small-pox, and it should 

 succeed in growing it in pure media, it might react very beneficially 

 on the practical application of vaccination. The more simple the 

 methods, the less chance will there be of the occurrence of those 

 unsuccessful cases which, even now, are rare exceptions. 



IT. Vaccinations against sheep-pox (la claveUe}. Sheep-pox, 

 being a disease very similar to human small-pox and very serious 

 from an economic point of view, the idea was conceived of fighting it 

 by methods similar to those used against small-pox. Since the 18th 

 century there has been practised on a large scale the artificial im- 

 munisation of sheep by the inoculation of the virus of the sheep-pox 

 (clavelisation) just as the variolisation of man was practised before 

 the discovery of cow-pox. For this purpose it was necessary to have 

 a considerable quantity of virus ; this was obtained by inoculating 

 sheep-pox into the skin of sheep. This inoculation was effected either 

 with a lancet or, according to Soulie's method 1 , by means of a Pravaz 

 syringe. The pustules, developed under these conditions, were gene- 

 rally of large size and capable of furnishing a considerable quantity 

 of the virulent lymph (claveau) used for immunisation. This fluid, 

 when gathered pure, and kept in a closed vessel protected from light 

 and heat, retains its virulence for a long time : unlike what is observed 

 in the case of vaccine, the addition of glycerine destroys the virulence 

 of the lymph pretty quickly. For use, the lymph is diluted with ten 

 times its volume of 2% borated water; the fluid thus obtained 

 is inoculated into the extremity of the tail or of the ear ; usually 

 a pustule, which remains single, is formed at the point of inoculation. 

 Clavelisation rarely sets up a generalised eruption which is always 

 serious and sometimes fatal. 



In France the law ordains the clavelisation of flocks in which 



sheep-pox appears; but it interdicts its practice in unattacked 



flocks ; it is easy to understand the reason for this ; in infected 



flocks all, or almost all, the sheep, gradually become ill and the 



[483] illness lasts for some time ; clavelisation diminishes both the duration 



and the gravity of the disease ; the mortality that it causes, although 



sometimes very great, the French sheep being very susceptible to 



sheep-pox, is always much less than that due to a natural contagion ; 



1 Medecine moderne, Paris, 1896, p, 441 



