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sion of yellow fever. So far as my information goes, this disease appears 

 incapable of propagation wherever tropical mosquitoes do not or are 

 not likely to exist, ceasing to be epidemic at the same limits of tempe- 

 rature and altitude which are incompatible with the functional activity of 

 those insects; while, on the other hand, it spreads readily wherever they 

 abound. From these considerations, taken in connection with my successful 

 attempts in producing experimental yellow fever by means of the mos- 

 quito's sting, it is to be inferred that these insects are habitual agents of its 

 transmission. It cannot be denied, however, that other such agents may 

 and probably do occasionally occur, but not being endowed with the same 

 facilities for rapid and extensive operation, their influence becomes insig- 

 nificant as compared with the action of the Cuban culex. 



