24 
REPORT OF THE MALARIA EXPEDITION. 
Owing to tlieir habit of breeding in tlie vessels of water which generally abound near 
houses, tlie pregnant females of Culrx need not fl)' so far to find water suitable for their eggs. It 
is possibly owing to this fact that, to judge by their more clumsy shape, they are less adapted for 
prolonged fliglit than Anophclri. 
(7.) Islot attracted hy lamps. It is often thought that gnats are attracted by lamps and 
candles, and perish in tliem. Thev may be attracted to liouses by lights burning in the windows; 
but we have never seen them hovering round the flames as moths and other insects do. Thev 
seem to bite less readily when there is a light in tlie room. 
(8.) Act of puncture. - On applying Anophch's in test-tubes to the skin we observed that the 
insects would sometimes make puncture after puncture without drawing any blood. In such cases 
however, each puncture was invariably followed bv the usual weal- showing that the insect 
always commences work bv injecting some of its saliva. It therefore follows that an Anopheles may 
inject some of its saliva (possibly containing the blasts of the Ha?mamoebidae) almost instantaneously 
— that is, before the victim feels the irritation and drives the insect away. 
It is certain that one can be bitten without knowing it - especially during sleep. Tims one 
often finds gorged gnats within the mosquito netting in the morning- -without having been at all 
conscious of their bites during sleep ; and it is therefore probable that those who sleep without 
nets may be much bitten without appreciating the fact. Even the weals often disappear in an 
hour or two ; so that not even the marks of the punctures need necessarily remain until next day. 
One of us thinks that much less irritation is caused if the insect is allowed to suck its fill, 
and has frequently observed the fact on his own person. This may be due to much of the 
irritating saliva having been sucked back during liaustellation. 
From several accounts it would appear that Anopheles hover over their victim less than Culex 
do, and consequently do not attract his attention so much by humming. 
People often imagine that gnats will not bite them ; but it seems to us impossible to accept 
such statements without sufficient experimental proof. What is more likely to be the case is that 
some persons do not much feel the punctures. The skin of some persons is not very sensitive ; 
and it is moreover possible that immunity may be acquired against the irritation of the injected 
salix a. Thus persons who have recenth' arrix ed in the tropics are well known to suffer more than 
old residents. This does not necessarily mean that the latter are less frequentl}' bitten, but, 
possibh', onlv that thev have become comparatively inured to the irritation.* 
17. Bionomical Questions still requiring Investigation. — The facts about gnats 
hitherto collected by no means exhaust the subject. We will indicate some of the more important 
questions which we found it impossible to deal with. 
(i.) Life in the dry season. -Between the rainy seasons many places in the tropics are 
extremely arid and free from pools suitable for Anopheles larva?. How then do the insects manage 
to continue the species from one rain)- season to the other r We may assume (i) that the larvae 
* It is however possible that the body may in the course of time produce some substance offensive to the insects, just as it 
may produce substances offensive to micro-organisms, 
