BY DR. A. JEFFERIS TURNER, M.D. LOND., D.P.H. CAMB. 121 
conclusion agrees with the epidemiology of plague as observed 
in Australia, may be learnt from the able reports issued 
by Dr. Ashburton Thompson and Dr. Ham. 
I have sufficiently transgressed on your patience, but 
did time permit I might give you details of yet other diseases 
of mankind spread by insects, for instance, the sleeping 
sickness, which is spread by a species of tsetse fly, and the 
spirillar fever of West Africa, which is spread by the bites 
of a species of tick. If diseases of domestic animals were 
included, we might study the tsetse-fly disease of cattle 
and horses in Africa, or the tick-fever of cattle, which is 
so unfortunately familiar in our own country. But this 
would be too large an undertaking for the present occasion. 
It is probable that the list of human diseases spread 
by insects will be extended in the future. Among diseases 
which are probably so spread, I may mention Dengue 
and Leprosy. The organism of Dengue is unknown; the 
reasons for connecting it with mosquitos are (1) its similarity 
to yellow fever, and (2) certain peculiarities in the spread 
of epidemic, which suggest that, in the beginning of an 
epidemic at all events, it is a house disease. The hypothesis 
that leprosy is spread by insect bites is a very old one. 
The leprosy bacillus has been long known, and can be 
easily demonstrated. But it cannot be cultivated outside 
the body, and unfortunately, it cannot be made to grow 
in ahy animal but man. The long period of latency renders 
it peculiarly difficult to trace the source of infection, and 
as the experimental method can hardly be applied, no 
speedy increase in our knowledge is to be expected. With 
regard to Dengue, the application of the experimental 
method used by Reed in yellow fever is much to be desired.* 
If the propagation by the mosquito were proved, we might 
stamp out such an epidemic as vexed us in 1904. Few 
things have struck me more this summer than the disgraceful 
number of mosquitos in the houses I visit in Brisbane. 
I say disgraceful, because by adequate screening of domestic 
water tanks (which is easy, but seldom done), or by the 
* Since writing this I learn that this has actually been carried out by 
American observers in the Phillipines, and the connection between dengue 
and a mosquito is now proved. 
