THE EETUEN TO VIRULENCE. 249 



great outbreaks of the epidemic, cases may be met 

 with of people attacked with boils, not fatal, but 

 resembling those of the deadly plague. Is it not pro- 

 bable that these boils contain an attenuated virus of 

 the plague, and that the passage of this virus into ex- 

 hausted bodies, which abound only too freely in periods 

 of famine, may restore to it a greater virulence ? 



' The same may be the case with other maladies 

 which appear suddenly, like typhus in armies and in 

 camps. Without doubt, the germs which are the 

 authors of these diseases are everywhere scattered 

 around, but attenuated ; and in this state a man 

 may carry them about him or in his intestinal canal 

 without great damage. They only become dangerous 

 when, by conditions of overcrowding, and perhaps of 

 successive developments on the surfaces of wounds, in 

 bodies enfeebled by disease, their virulence is rein- 

 forced.' 



