112 THE CONTAGIOUS TYPHUS 



the most part a favourable soil, and a special 

 predisposition amongst animals to receive and 

 propagate it ; thirdly, what is called an epi- 

 demic or epizootic genius that is to say, a 

 particular state of the atmospheric elements, 

 or the air, which hitherto has escaped our 

 analyses, and whose morbific properties vary 

 in their degrees of intensity. Thus the epi- 

 zootic genius of 1711, the terrible one of 1750, 

 and the one which now diffuses its conta- 

 gious miasma, have differed in some of their 

 virulent conditions. 



However that may be, it will be sufficient 

 to glance back at the past to assure ourselves 

 that, in general, epizootics have been coinci- 

 dent with some violent change of season, such 

 as extreme droughts, or superabundant rains ; 

 that is to say, when the cattle, disturbed in 

 the physiological conditions of their health, 

 have become favourable to the incubation of 

 the miasmatic leaven scattered through the 

 air, or else when these animals were living 

 under irregular conditions, and had to endure 

 unwonted fatigues and privations, as in the 

 folds of campaigning armies, for instance. 



These epizootics have appeared to depend 



