500 
Stegomyia fasciata 
living S. cerevisiae and sterile extracts of brewers’ yeast to that which 
separates living fronr dead cultures, or sterile filtrates of bacteria. It 
is not quite so definite, however, as the larvae do make progress in 
solutions of autofyzed yeast extract, whereas throughout the whole 
course of the experiments no larval progress has occurred in sterilized 
cultures of bacteria or sterile filtrates. The reason for this difference 
is not obvious and it seems possible that by some system of concen¬ 
trating and extracting bacterial cultures analogous to the autolyzing 
process with yeasts, the difference might be eliminated. 
The effect of the presence of moulds on larval growth. 
Although no experiments were planned with a view to testing the 
influence of moulds, their occurrence in both sterile and bacterially 
infected tubes was so frequent in some of the experiments that a con¬ 
siderable amount of general observation was possible. The impression 
gained during the progress of the research was that moulds were inimical 
to larval development, but a careful consideration and comparison of 
the notes show that the fatality which so frequently followed their 
appearance in the experimental tubes cannot be clearly demonstrated 
as due to their presence. In a few cases of rapidly spreading surface 
moulds it is extremely probable that they were an accessory, if not the 
actual cause of death, and in Experiment XXII an instance of mortality 
apparently due to moulds occurred in tubes Nos. 4 and 5 of the distilled 
water series. What does, however, appear quite definite is that they 
are of no service whatever to the larvae as a source of food supply. 
In fact it seems reasonable to suppose that they may compete with the 
larvae for whatever supply of nutriment is available. Although the 
evidence on this point is not altogether consistent, in Experiment XXII 
it appears quite negative, there were several instances in which fully 
grown larvae died in tubes where moulds had developed. In a few 
cases one or two out of several of the larvae succeeded in completing 
their development, the others dying rather inexplicably if the moulds 
were not implicated. Two or three instances occurred of moulds grow¬ 
ing from the mouths of dead larvae, as though swallowed spores had 
developed in the alimentary canal; while there is of course no evidence 
that the development of the mould preceded death, the spores must 
presumably have been ingested by the living larvae. Notes referring 
to the presence of moulds will be found in Experiments XXI, XXII 
and towards the close of XVII and XXIII. 
