F. M. Howlett 
483 
The effect of the hot tube was very much less when it was held as 
in Fig. 4 in such a way that most of the hot air from its surface passed 
clear of the insects, indicating that it is the current of heated air and 
not the radiant heat from the tube which exerts the more influence. 
The eagerness with which the mosquitoes attacked the tube slackened 
as the water cooled. 
Fig. 4. 
One or two easily observed facts may be considered in conjunction 
with the above results. 
Mosquitoes often hover in a cloud over one’s head, but this cloud is 
always columnar in shape, never flattened, and is well seen only when 
the air is still and the currents from the body are rising straight up from 
it. Such clouds are most often noticed towards the cool of the evening, 
when mosquitoes may also be seen hovering over almost any hot body, 
particularly if its form is such as to concentrate the rising air into a 
fairly narrow column. 
Mosquitoes rarely attack Amphibians and Reptiles, while among 
warm-blooded animals birds (whose body-temperature is above 100° F.) 
are I believe quite as subject to attack as are Mammals, particularly if 
we take into account the relative degree of protection afforded by 
feathers. Horses are often much annoyed by mosquito bites. 
With at least one notable exception {S. scutellaris), mosquitoes 
are nearly always most active at night or when the atmosphere 
begins to cool down towards sunset; I am speaking now of the Plains 
of India. In the hills where the air temperature is lower, I have 
fancied that their active period was much less definite and restricted, 
but this is merely a general impression based on small experience. The 
extreme ferocity of mosquitoes found in very cold climates is notorious, 
and has never really been explained. 
The conclusions we may draw from the observations and experiments 
here outlined are (a) that the bite of a mosquito is a reaction to the 
stimulus provided by a hot surface, {b) that the mosquito is attracted to 
