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postulated admission that distinct species of mosquitoes might differ in 

 their aptitude to retain in a fertile condition special disease germs, picked 

 up by their proboscis during the operations of stinging and of drawing 

 blood and that it should be true with regard to some particular inoculable 

 germ and not with regard to others. Without this admission it would be 

 impossible to claim for the mosquito the privilege of transmitting Yellow 

 Fever when there is nothing to prove that Smallpox, Syphilis and other 

 inoculable diseases have ever been so transmitted. The first confirmation 

 of my assumption occurred in the following manner: Mosquitoes which 

 presumably had never come in contact with Yellow Fever patients were 

 allowed to sting and fill themselves with blood from healthy immune sub- 

 jects, and then introduced into sterile tubes containing agar-agar jelly. 

 Thus imprisoned the mosquitoes discharged their excrements upon 

 the sides of the tubes, and after fluttering about would stand upon the 

 jelly and prick its surface with the point of their proboscis. After three or 

 four days they died of inanition, and their cadavers being left inside of 

 their respective tubes, the cotton plugs were covered with wax to prevent 

 the entrance of small insects. The tubes so prepared were kept several weeks 

 under observation with the remarkable result that not a single colony or 

 fungus appeared upon the agar-agar jelly. The same experiment having 

 been repeated with mosquitoes which had been allowed to sting Yellow 

 Fever patients, isolated colonies of M. tetragenus versatilis (Sternberg) 

 made their appearance upon the agar-agar jelly, at the end of 24 or 48 

 hours, apparently in pure cultures : for the few bacilli or cocci subsequently 

 encountered in some of the cidture tubes, might well be attributed to 

 accidental infections during the manipulations. 



Until recently, I had considered three varieties of our Havana day- 

 mosquito which differ but little except in size (the large, the medium sized 

 and the small C. mosquito), as equally adapted for my inoculation expe- 

 riments, though I had long since observed that my inoculations with the 

 smallest species had been more frequently followed by pathogenic results. 

 A recent observation appears to throw more light upon this point. On the 

 3rd of June two mosquitoes : one medium size and the other belonging 

 to the small species — were made to sting a Yellow Fever patient on the 

 6th day of his illness. On the 6th of the same month these mosquitoes were 

 applied to a young unacclimated Spaniards, who was taken ill on the 23rd 

 with a mild fever (maximum 38-5° C. and defervescence on the 5th day) 

 with distinct albuminuria from the 3rd to the 13th day. On the 29th two 

 fresh mosquitoes (one medium sized and the other small) were allowed 

 to sting and fill themselves from this patient and two hours later both 

 these mosquitos and also the two that had died after their sting on June 

 3rd were taken by me to Dr. Santos Fernández' Laboratory, where with 

 the assistance of our able bacteriologist Dr. Davalos, the following inves- 

 tigation was carried out : the two live insects having been killed by dropping 



