E. E. Atkin and A. Bacot 
483 
larvae of Aedes are largely bottom feeders and may be seen vigorously 
working over dead leaves and vegetable debris with their mouth organs, 
apparently removing the fungoid growth which covers them. 
Boyce and Lewis (1910) showed that the presence of mos(puto 
larvae added to clean water led to an increase in the number of bacteria. 
Unfortunately the authors have not put on record the methods they 
pursued in arriving at this result, consequently we are left in doubt 
as to whether certain very necessary precautions to avoid fallacies 
were taken or not. For instance it is not stated in what stage or from 
what source the larvae they added to the clean water were taken, 
while, unless these factors were carefully controlled, there would be (as 
pointed out by the authors of the Carnegie Monograph on the Mos¬ 
quitoes of North and Central America 1912) grave danger of the intro¬ 
duction of organic matter voided from the larval gut. The fact that 
an increase of bacteria followed the introduction of the larvae is there¬ 
fore no valid argument against the popular belief of the cleariirg action 
of the mosquito larvae, unless the larvae had been introduced imme¬ 
diately after hatching, or just after a moult; the hatching of the eggs 
or moulting of the larvae having taken place in comparatively large 
quantities of clean water. 
Bacot (1916) carried out a number of carefully planned experiments 
in Freetown, Sierra Leone, using newly hatched larvae of S. fasciala, 
with a view to ascertaining the amount and nature of the food con¬ 
sumed by the larvae and whether bacterial development in the breeding 
pans was a factor in the problem. He found that there existed a very 
definite relation between the development of bacteria and the growth 
of the larvae. Subsequently, on his return to England, he discovered, 
as detailed in a footnote to his report (see Experiments I and II), that 
water highly charged with organic matter, and swarming with bacteria, 
exerted a powerful stimulus to hatching on eggs which had not responded 
to immersion in clean water. The suggestion in his report that the 
bacteria themselves formed food for the larvae was based on the clear¬ 
ing action they displayed in water, rendered turbid by its enormous 
bacterial content, in conjunction with the fact that the gut-contents of 
larvae, taken from this water, showed only a few bacteria per field in 
contradistinction to the crowded fields displayed when water in which 
the larvae swam was examined. It being deemed impossible that 
bacteria could be excluded when the larvae were sweeping small par¬ 
ticles of matter into their mouths, the explanation of their scarcity 
must therefore depend upon their rapid digestion. 
Parasitology ix 
32 
