234 COW-POX. 



hard winds of spring, after a wet winter, are supposed to 

 have the same influence. I have, however, seen the disease 

 in the autumn and middle of winter after a dry summer. The 

 disease is occasionally epizootic, or prevalent at the same 

 time in several farms at no great distance, more commonly 

 sporadic or nearly solitary. It may be seen sometimes at 

 several contiguous farms ; at other times, one or two farms, 

 apparently under like circumstances of soil, situation, etc., 

 amidst the prevailing disease, entirely escapes its visitation. 

 Many years may elapse before it recurs at a given farm or 

 vicinity, although all the animals may have been changed in 

 the meantime. I have known it occur twice in five years in 

 a particular vicinity, and at two contiguous farms, while at a 

 third adjoining dairy, in all respects similar in local and other 

 circumstances, it had not been known to exist for forty years. 

 It is sometimes introduced into a dairy by recently purchased 

 cows. I have twice known it so introduced by milch heifers. 

 It is considered that the disease is peculiar to the milch cow 

 that it occurs primarily while the animal is in that condi- 

 tion and that it is casually propagated to others by the 

 hands of the milkers. But considering the general mildness 

 of the disease, the fact of its being at times in some indivi- 

 duals entirely overlooked, and that its topical severity de- 

 pends almost wholly on the rude tractions of the milkers, it 

 would perhaps be going too far to assert its invariable and 

 exclusive origin under the circumstances just mentioned; yet 

 I have frequently witnessed the fact that sturks, dry heifers, 

 dry cows, and milch cows milked by other hands, grazing in 

 the same pastures, feeding in the same sheds and in contigu- 

 ous stalls, remain exempt from the disease. Many intelli- 

 gent dairymen believe that it occurs more frequently as a 

 primary disease among milch heifers; but I have not been 

 able to confirm this remark by my own observation. It does 



