260 LOUIS PASTEUK. 



proved that the countries subject to splenic fever have- 

 an argillaceous -calcareous soil, and that the disease is- 

 unknown in schistose and granitic soils. The contrast 

 of the results, in relation to such differences of soil, is 

 seen sometimes in the Department of the Aveyron, 

 between the right and left side of one and the same 

 road or watercourse. 



May we not now in all confidence assert that, if 

 the cultivators choose, splenic fever may soon be a 

 thing of the past among their animals, their shep- 

 herds, and among the butchers and the tanners of 

 the towns, because splenic fever and malignant pus- 

 tule are never spontaneous ? The disease exists only 

 where it has been sown, or where it has been diffused 

 by the unconscious instrumentality of the earth-worm. 



The progress of vaccination will also contribute to 

 the disappearance of splenic fever ; for this preventive, 

 if extensively used, as there is no doubt it will be, must 

 end by establishing a race of domestic animals which, 

 having all sprung from vaccinated parents, will in conse- 

 quence be more resistent to the disease in its worst form. 

 It will be with them in relation to splenic fever as it 

 is with ourselves in relation to small-pox. It is a well- 

 known fact that the ravages of small-pox are much 

 less considerable in our days than when it first 

 appeared in Europe. It is difficult not to attribute 

 this, at least in part, to the prevalence of vaccination. 



In the populations where small-pox is introduced 



