( Hi ) 



certain conditions the hatching of a batch of eggs might be 

 spread over two or three months, the fully developed larvae 

 within the eggs awaiting the occurrence of some stimulus before 

 breaking out of the shell. A fall in the water temperature 

 of about 7° to 10° F. acted as a stimulus, but usually only 

 on a moderate percentage of the resting eggs. The addition 

 of foul, contaminated water to the breeding-pans afforded a 

 much more comprehensive stimulus. 



A research, in which Dr. E. E. Atkin joined, carried out at 

 the Lister Institute since Mr. Bacot's return from West 

 Africa — a full account of which it is hoped to publish shortly 

 — threw further light on the subject. It showed that, under 

 sterile conditions, the eggs very generally though not in- 

 variably failed to hatch, until the water, or the medium in 

 which the eggs were resting, was infected by living organisms. 

 Various reagents failed to produce a corresponding effect, nor 

 was a bacterial filtrate any more effective than a culture killed 

 by heat. 



Mr. Bacot showed tubes containing eggs that had been 

 sterilised, and had remained for a month without hatching in 

 sterile distilled water, to which 15 per cent, of the filtrate of 

 a culture of Bacillus coli had been added. He demonstrated 

 that the addition of a minute quantity of yeast organisms from 

 a culture tube caused the eggs in one of the tubes to hatch 

 within 10 to 15 minutes. In a duplicate tube, which had 

 been infected by a species of bacteria shortly after the be- 

 ginning of the experiment, the eggs had hatched, and this 

 tube now contained a number of dead adult mosquitoes which 

 had been bred out. 



The question to which an answer was sought was the exact 

 nature of the stimulus exerted by the organisms and the 

 manner in which it affected the larvae lying within the eggs. 



In answer to questions by the President, Mr. Bacot said 

 (1) that the ova when laid in dirty water became covered with 

 bacteria, and that by sterilising the ova he meant clearing 

 the shell of such bacteria ; (2) that the larva could live in the 

 dried egg for upwards of 8 months, and had been stated to 

 be able to do so for 18 months, while in water they might lie 

 as long as 5 months without hatching. 



