244 Facts relative to Cynanchc Trachealis. 



It has usually made its first appearance in the last of 

 autumn, or beginning of winter. There is a variety of 

 the disease, of which I shall have occasion to speak 

 hereafter, that I have seen at all seasons, but which is 

 seldom attended with danger. It is most prevalent, \ 

 think, between the first of December and last of Janu- 

 ary, but continues to occur, with abated frequency, till 

 the return of warm weather. 



Query 6. What appear to be the most common 

 causes of the disease ? 



The sensible qualities of the air have considerable 

 influence in producing it. Sharp keen weather, especi- 

 ally with sleet or snow, have often multiplied cases of it, 

 and it is evident that the children of certain families have 

 a peculiar liability to the disease ; but, as a recurrence of 

 the same sort of weather, at the same seasons, in other 

 years, is often unattended with a like recurrence of the 

 disease, it follows that other agencies must be con- 

 cerned in its production. Whether these are to be 

 sought after in the predisposing tendency of preceding 

 seasons, or among the occult properties of the existing 

 state of the atmostphere, are probably enquiries of con 

 siderable intricacy. 



Query 7. Between what ages lias it generally she 

 itself? 



It has been generally confined to children, and parti- 

 cularly to those within the first three years of infancy ; 

 but in 1799, when the disease was tpidemical in this- 



