444 the president's address. 



or even impossible to obtain a sufficient number of experimental 

 animals for such a protracted series of experiments. 



From Prof. Kleine's experimental results it is evident that the 

 trypanosome of nagana, and doubtless of sleeping sickness also, 

 does undergo a cycle of development in the tsetse-fly, and the way 

 is now open for the microscopist to rush in and to observe what 

 becomes of the parasite in this long period that elapses between 

 its being taken up by the fly and being given out again. We 

 may expect that a fascinating and wonderful history will be made 

 known of the transformations and migrations, the amours and 

 the increase of the trypanosome in the bowels of the unconscious 

 tsetse-fly. And we seem now to be in sight of a solution to 

 the baffling problem of the transmission of diseases caused by 

 trypanosomes. 



The third disease I have chosen for my discourse, namely, 

 yellow fever, is one sufficiently well known to every one, by 

 repute at least. There is no need for me to describe at length 

 the dreaded " Yellow Jack," a malady often fatal, and always 

 excruciatingly painful. The connection of this disease with 

 mosquitoes has long been suspected, and has recently been proved 

 conclusively by both the American and French commissions sent 

 out to study the disease. The mosquito in this case is neither a 

 Culex nor an Anopheles, but one belonging to a distinct genus, 

 namely, Stegomyia Jasciata, sometimes called the Tiger-mosquito. 

 It has been proved conclusively that the mosquito does transmit 

 yellow fever, and it has also been proved that the disease is not 

 communicated by direct infection or contagion through con- 

 taminated clothes or dwellings. And here let me draw attention 

 to one great obstacle to conducting experiments on yellow fever — 

 the fact, namely, that the disease is not communicable to animals, 

 but only, so far as is known, to man. Hence experimental studies 

 on the disease could only be performed on men who offered them- 

 selves voluntarily for this purpose. Such experiments were 

 sometimes negative, sometimes positive, in their result ; in the 

 latter case, of course, the subject of the experiment acquired the 

 disease, and in one case at least died of it. It would require 

 the pen of a Shakespeare or a Milton to do adequate justice to 

 such devotion on the part of these brave men to the cause of 

 science and humanity. 



By numerous carefully devised experiments a number of 



