Microbic Diseases Individually Considered. 207 



by Lydtin were unsuccessful, there is reason to believe 

 that, under natural conditions, the virus gains entrance 

 by the digestive canal. 



The virulent matter ingested by healthy pigs will 

 consist especially of the intestinal dejections of the 

 diseased. Lack of proper attention to the feeding 

 troughs, and defective conditions of the pens (ventila- 

 tion, lighting, cleanliness) are of a nature to favor the 

 propagation of rouget, as well as of other diseases of 

 the pig. 



Adult hogs, especially those of the improved breeds 

 (English), are most liable to contract the disease ; 

 young pigs and those of native breed are more resist- 

 ant. 



Attenuation. Vaccination. — Rouget of the pig be- 

 comes well acclimated in the pigeon and the rabbit, 

 and in these two species acquires great virulence ; but 

 whilst its repeated passage through the organism of 

 the pigeon renders it more active for the pig, passage 

 through the rabbit, on the contrary, diminishes its 

 virulence for the pig. This attenuation, after a certain 

 time, is such that the virus coming from the rabbit 

 no more kills the pig; it, however, makes it sick and 

 confers immunity on it against strong virus. The at- 

 tenuation thus obtained persists in cultures afterward 

 made in ordinarv bouillon and these cultures can be 

 used to vaccinate the pig. 



In practice two vaccines only are employed, and 

 these in succession at ten days interval ; a feeble vac- 

 cine is used first and then a second, the virulence of 

 which is much stronger. 



Young pigs being much less susceptible to the dis- 

 ease and therefore to the virus, the period of youth 



