498 
Stegomyia fasciata 
observed, but the progress was not continuous and both larvae died 
some 50 days later without having completed their larval development. 
Experiments XII and XIII were designed with a view to trying 
sterile media composed of substances more likely to be met with by 
mosquito larvae under natural conditions than those normally used for 
bacteriological purposes. Tubes containing water in which horse dung 
had been steeped 48 hours previously and a broth made from dead 
insects—chiefly flies—were used. The series afforded but little evidence 
bearing on the original purpose of the tests owing to the infection of 
the tubes by obscure species of bacteria whose presence was difficult to 
detect, and such evidence as was forthcoming was negative. The tests 
convinced us, however, of the unsuitability of these media which were 
likely, owing to the sources from which the nutriment contained in 
them was drawn, to harbour sporing bacteria. 
Particulate matter. One of our colleagues suggested the possibility 
of the necessity of particulate matter in the medium as it seemed 
possible that larvae swimming in a true fluid might be unable to pass 
it through the alimentary system in the absence of solid particles in 
the intestine. We accordingly added powdered animal charcoal to a 
number of tubes of a solution of autolyzed yeast in distilled water 
(Experiments XVI and XVII) with apparent success at the outset, as 
the larvae not only ingested it—the dark gut content being clearly 
visible—but made quicker progress than others in the same media 
without the charcoal. The advantage did not, however, continue and, 
although one reached the pupal stage, no adults were reared; on the 
other hand, as already recorded, one adult was reared from a sterile 
tube of the yeast extract solution, without the charcoal. It is also to 
be noted that the insect broth which contained much solid matter also 
failed, under sterile conditions, to confer any advantage after the first 
few days. 
A few trials were carried out to test if milk acidified to such a degree 
that the colloidal particles of the casein were increased in size but not 
precipitated and white of egg precipitated as very minute particles, 
would afford the necessary pabulum for the larvae. After sterilization 
small quantities of these preparations were added to media in which 
eggs had already hatched, but in which the larvae were making no 
progress, or the larvae were transferred by Pasteur pipette to tubes 
containing milk or white of egg in this form. Examples will be found 
in Experiments XIII, XVIII, XIX and XX. In no case did the 
addition or presence of the substances enable the larvae to develop 
