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a little ether upon the cotton plugs that closed their respective phials, the 

 head of each mosquito was detached from its body and inserted, with due 

 precautions, in a tube of sterilized broth. The two tubes planted with the 

 mosquito heads of June 3rd were placed in the thermostat at 37° C, while 

 the other pair of tubes were kept at the room temperature (28-30° C). 

 The following day signs of germination were apparent as a sediment in the 

 tubes containing heads of the small mosquitoes of June 3rd and 29th but 

 not in the others. After 48 hours, the growth being sufficiently advanced, 

 microscopical preparations were made and showed a micrococcus in tetrads, 

 which in agag-agar plate-cultures and inoculations in gelatine was 

 identified as my M. tetragenus febris flavae ("versatilis" Sternberg) ; no 

 other bacteria having been obtained from these tubes. The two other tubes 

 containing the heads of the medium sized mosquitoes of June 3rd and 29th 

 never showed any signs of germination during the three weeks that they 

 were kept under observation. 



From this curious investigation, I infer that while the parts that con- 

 cur in the formation of the head and proboscis of the Havana day-mosquito 

 possess bactericidal properties for the generality of bacteria and fungi that 

 grow in broth or upon agar-agar, an exception must certainly be made with 

 regard to the M. versatilis which develops with unwonted vigor from the 

 head and proboscis of the small culex mosquito, though under similar cir- 

 cumstances, it does not appear to do so from that of the medium sized 

 species. 



As regards the M. tetragenus versatilis, which I have so often met in 

 my investigations upon Yellow Fever finger-blood and blister serum, I 

 cannot yet claim for it a decided and absolute proof of its etiological sig- 

 nificance, though strong presumptions have been gradually accumulating, 

 and the results which I have just described add a new argument in its 

 favor. 



What I wish particularly to point out is the strong evidence which T 

 have collected in support of my theory: that Yellow Fever may be trans- 

 mitted by certain species of mosquitoes which are peculiar to the Yellow 

 Fever zone, and may be transported to other regions where a suitable tem- 

 perature and barometrical pressure prevail during certain seasons of the 

 year; as also that the non-transmission of the disease in certain localities 

 may be due to the absence or scarcity of that particular kind of mosquito. 



In the course of 13 years, I have now inoculated ninety persons all 

 of whom were presumably susceptible to Yellow Fever. In comparing in 

 my notes, the proportion of inoculations which were followed, within 3 to 

 25 days, by a non-albuminuric or simple albuminuric fever I find them dis- 

 tributed as follows: 



