484 
The Bitmg of Mosquitoes 
the hot surface mainly by the warm air rising from it, and (c) that the 
strength of the reaction is, within certain limits, proportional to the 
“ differential temperature ” of the surface, i.e. the difference between its 
temperature and the general air-temperature at the time, and that this 
difference must be positive. 
If this last conclusion is correct we should expect to find that 
mosquitoes bite only when the shade-temperature is below the body- 
temperature of the victim. My own imperfect recollections incline me 
to the belief that this may actually be the case. Careful observations 
carried on for a month or two in hot weather would probably give fairly 
conclusive evidence on the point, and would enable us to estimate the 
relative importance of the differential effect and the general increase in 
energy often associated with a rise of temperature. 
While it seems certain that temperature is a dominant factor, it is 
more than possible that other induences may affect mosquito-attacks. 
Such are, for instance, light, the pressure, humidity, and electrical con¬ 
dition of the atmosphere, to say nothing of the physiological condition 
of the various organs and tissues of the insect itself None of these 
have been taken into consideration. It would be rash to deny any 
importance to the sense of smell, in view of the vital influence it exerts 
on the lives of some other Diptera, and of the protective action of 
kerosene, citronella, and many essential oils when rubbed on the skin. 
An interesting point is the alleged comparative immunity from 
mosquito-bite enjoyed by certain individuals. 
Study of the blood-sucking Diptera leads one more and more to the 
conclusion that in many respects they may be justly defined as mere 
“ bundles of reflexes.” The result of actual observation, as well as 
general phylogenetic considerations, make it extremely improbable that 
their reactions are of an ideirtical nature throughout the different 
families, and their investigation from this point of view might well lead 
to some improvement in methods of control. 
