146 BOAED OF AGRICULTUKE. 



and simultaneous appearance over a wide extent of territory, 

 would show that they are often due to other influences than 

 contagion, in the sense at least just given. Still, under cir- 

 cumstances not yet recognized, certain diseases may prevail 

 in an epidemic form, and prove contagious at one time, which 

 at another time do not possess this character, or do not make 

 it manifest in the usual manner. If we may trust the observa- 

 tions which have been made, epidemics of this very disease 

 under consideration have spread from time to time over large 

 portions of Europe, at one season being highly contagious, 

 while at another they have not been thus characterized. It is 

 only by patient and close investigation that we can hope fully 

 to solve the problems connected with this question of con- 

 tagion. 



There are other peculiarities of epidemics which deserve 

 notice. Thus, while all epidemics of the same disease may 

 present well-established features, these may vary greatly in 

 different years. Sometimes the symptoms which they exhibit 

 are very mild, and terminate quickly in complete recovery, 

 while at other times they are exceedingly severe, assume a 

 chronic form, or tend to a rapid fatality. In most of the 

 catarrhal epidemics of Europe it has been observed that the 

 young are the most susceptible, and the aged the least so ; 

 that the spring months and very wet autumns are the most con- 

 ducive to the disease ; that where large numbers of horses are 

 collected in crowded cities and towns, and where proper atten- 

 tion cannot be paid to hygienic laws, there the malady exerts 

 its full force. Then, again, in some epidemics the disease 

 confines itself almost entirely to the nasal passages, while 

 in others it attacks the air-passages generally, expending 

 its power upon the lungs and 'other important organs, 

 whereby we may account for the various names and treat- 

 ment to which it has been subjected. Formerly catarrhal 

 epidemics were eminently febrile, that is, of an inflammatory 

 character, and in many cases admitted of bleeding ; but more 

 recently they have shown typhoid symptoms, that is, they 

 have been marked by great debility, in which the letting of 

 blood has been contra-indicated. 



We have been singularly exempted in this country from the 

 prevalence of epizootics, but we cannot hope always thus to 



