494 
Stegomyia fasciata 
emerged and died before the 12th day; both tubes were then inoculated 
from a living culture of S. cerevisiae and all the remaining eggs hatched 
during the night. 
In spite of the foregoing negative evidence we thought it desirable 
to test the matter further, because it seemed possible that the failure 
might be due to either too high a temperature in the sterilization pro¬ 
cess or to the yeast extract not being sufficiently fresh—some days 
having been allowed to elapse between preparation and use. 
With this object Experiment XXIV was planned. A number of 
tubes of distilled water containing eggs were used on the fifth day after 
the addition of the eggs. Cultures of B. coli, S. aureus and autolyzed 
extract of brewers’ yeast which had been autoclaved (120° C.) were 
used, also cultures of B. coli and S. aureus which had been killed by 
steam heating at 100° C., a culture of B. coli killed by chloroform and 
a sterile filtrate of B. coli. The addition to the tubes was 6 %, except 
that in one of the tubes only 2J % of the yeast extract was added, but 
this alteration made no difference to the result. It will be seen that in 
contradistinction to the earlier results the sterilized cultures and yeast 
extract were effective, but not the filtrate. This last was several weeks 
old at the time of use, but fresh filtrate had been used in the earlier 
trials without effect. It is interesting to note that the eggs were slower 
in responding to the S. aureus than to B. coli in all four tubes. 
The results were so generally at variance with those in the earlier 
trials that it seemed probable that the difference must lie in the eggs. 
With a view to testing this hypothesis advantage was taken of several 
tubes of distilled water in Experiment XXIII in which eggs had been 
lying dormant for 100 days. These were tested by adding a quantity 
equal to about 3 % of a living culture of B. coli, autolyzed yeast steri¬ 
lized by autoclave and B. coli sterilized by autoclave, the last two being 
from the same tubes as the additions to the tubes in Experiment XXIV. 
It will be seen that the results again differ, being more in line with the 
early trials, but not quite in conformity. There seems no doubt but 
that the susceptibility of the eggs varies greatly while it is also con¬ 
sistent with the results to suppose that the cultures but not the filtrate 
used—possibly because of their freshness—were more effective. 
A further trial. Experiment XXV, was carried out to test the watery 
extract of yeast as against an autolyzed one, and both as against living 
cells from a culture of Saccharomyces cerevisiae on wort agar. 
As a whole this test shows clearly that while, for these particular 
eggs, the autolyzed extract and the living cells were almost equally 
