E. E. Atkin ane a.. Bacot 
493 
amples of hatching in apparent response to moulds occurred in Experi¬ 
ment XXII. 
The most plausible suggestion as to the nature of the stimulus which 
induces the eggs to hatch would seem to be that of a scent which pene¬ 
trates to the larvae lying dormant within the egg shells causing them 
to make vigorous movements resulting in the uncapping of the egg. 
There is, however, a difficulty in the way of the acceptance of this 
theory, owing to the partial or entire failure in some cases of killed 
cultures or filtrates of B. coli and sterile yeast extracts to bring about 
the hatching of the eggs. This subject is dealt with in greater detail 
in the following section. 
The effect of killed bacterial cultures; sterile filtrates of B. coli 
and extracts of brewers' yeast. 
Until nearly the close of the experimental w'ork no results had been 
obtained from the addition of killed cultures and sterile filtrates of 
B. coli (see Experiments XIV, XXI and XII). On one occasion 
(Experiment IX) the addition of about 17 % to 20 % of a sterile auto- 
lyzed extract of brewers’ yeast caused eggs which had been lying 
dormant in a tube of peptone water for a month to hatch within one 
hour, but the larvae died within a few minutes. In Experiment XI 
about 8 % of a sterile watery extract of brewers’ yeast was added on 
the 15th day to a tube of peptone water containing dormant eggs, but 
no action having resulted within a week, the tube was inoculated from 
the culture of a species of yeast isolated from a human throat. The 
eggs hatched during the following night. 
When sterilized eggs were pipetted into tubes of distilled water 
containing 2 % or 3 % of an autolyzed extract of brewers’ yeast (Ex¬ 
periments XVI and XVII) hatching was not general, nor did hatching 
occur any more freely than in different media in the other tubes. In 
Experiment XVII larvae continued to hatch out from dormant eggs 
over long periods. In one case eggs that had remained dormant for 
over 90 days'hatched without any interference with the tube. While 
in another instance eggs that had been resting for 126 days hatched on 
the addition of boiled distilled water to three tubes which were almost 
empty owing to evaporation. 
Experiment XXL None of the eggs in two tubes of an autolyzed 
extract of brewers’ yeast solution (3 % in distilled water) hatched 
within 96 hours, but one larva emerged in each tube within 120 hours. 
In one tube no more eggs hatched, but in the other two or three larvae 
