INFLUENCE OF ENVIRONMENT 



247 



done the same. It is well known that poisons applied in small quantities 

 act as stimulants. Two years ago I successfully used bacterial cultures 

 producing H2S as an attractive agent for mosquitoes. 



t Highest score — 10. 



* Strong smell of hydrogen sulfide. 



** Two Anopheles larvae died before full grown. 



"At the time when the Culex and Anopheles larvae were taken in the 

 pond, no determinations of ammonia and albuminoid nitrogen were 

 made, but the sample taken before showed 0.4 ppm., NH3-N and 4.1 

 ppm. albuminoid-N, while the sample taken after, when larvae were still 

 present, contained 0.5 ppm. NH3-N and 4,3 ppm. albuminoid-N. The 

 albuminoid-N tends to show a slight pollution, probably from street 

 washings. The data presented seems to indicate that our conclusion 

 reached formerly (20) was correct, namely that food supply for larvae 

 is the main cause governing breeding. This food supply in turn is de- 

 pendent on the chemical composition of the water. Atkins (1), in study- 

 ing the phosphate content of the water in relation to the growth of 

 algal plankton, shows that phosphate is the limiting factor for the 

 growth of diatoms. Atkins and Harris (2) found that an accumulation 

 of phosphate results in a tremendous increase of phytoplankton. These 



