340 



J. W. SCOTT MACFIE — A NOTE ON THE ACTION OF COMMON 



It may therefore be assumed as probable that the larvae of S.fasciata thrive 

 best in a medium whose salinity is about 0*012 per eent. NaCl. In order to 

 determine whether the higher pereentage of salt present in the lagoon would 

 prove injurious to them, three samples of water eontaining larvae from domestic 

 utensils was selected, and salt was added to them until the salinity of each was 

 0*026, the same percentage as was found to be present in the lagoon water at 

 the Iddo bridge. No perceptible action was observed on the larvae, which 

 remained healthy and active during the succeeding four days. The percentage 

 of salt in two of the samples was then raised to 0*112, as in the lagoon water 

 under Magazine bridge. The larvae seemed to be affected somewhat by this 

 degree of salinity, and tended to remain for long periods at the bottom of the 

 jars. By the seventh day all those in the one sample were dead, and only one 

 remained alive in the other. The last larva died on the eighth day. 



Experiments with Solutions of 0*5 per cent. NaCl and upwards. 



The foregoing preliminary experiments suggested that it might be of some 

 interest to determine the effects of various strengths of salt solutions on the larvae 

 of S. fasciata. In order to exclude the factor of precipitation, the experiments 

 were in the first instance carried out in clean water. 



For this purpose ten mature larvae were placed in each of six jars containing 

 respectively 0*5 %\l%,2%,S% i 4 %, and 5 % NaCl solutions. The results 

 of the experiments are shown in detail below : — 



Table I. 



NaCl. 



0-5 % 



1 o/c 



2% 



3% 



4% 



5 % 



Oct. 12. 11 a.m. 



10 L. 



10 L. 



10 L. 



10 L. 



10 L. 



10 L. 



,, 1 p.m. 



9 L., i r. 



10 L. 



9 L.. 1 P. 



10 L. 



1 L., 9 dead L. 



All dead. 



.. 3 p.m. 



9 L.. 1 V. 



10 L. 



9 L., 1 P. 



7 L., 3 dead L. 



All dead. 





,. 5 p.m. 



9 L., J P. 



10 L. 



9 L.. 1 P. 



6 L.. 1 dead L. 







., 11 p.m. 



9 L., 1 P. 



10 L. 



9 L.. 1 P. 



All dead. 







Oct. 13. 



7 L., 3 P. 



7 L., 3 P. 



8 L., 1 P., 1 



dead L. Three 



larvae almost 



inert. 









Oct. 14 



G L., 4 P. 



7 L., 2 P.. 1 M. 



4 L.. 1 P., 



3 dead L. 









Oct. 15 



5 L., 2 P.. 3 M. 



6 L., 3 M. 



All dead. 









Oct. 16 



5 L., 2 P. 



6L. 











Oct. 17 



5 L.. 2 M. 



4 L.. 2 dead L 











Oct. 18 



•-> L. 



4L. 











Oct, ID 



5 L. 



4L. 











Oct. 20 



5L. 



3 L., 1 dead L. 











Oct. 22 



5 L. 



1 L., 2 dead L. 











L = Larva. P = pupa, M = adult mosquito. 



The effects of the different solutions on the larvae varied directly with their 

 strengths. In 5 % NaCl all the larvae had died within two hours, in 4 % within 

 four hours, and in 3 % within twelve hours. In 2 % NaCl solution all had died 

 within three days ; in 1 % during the ten days for which the experiment was 

 continued, five larvae died, four pupated and hatched, and one remained alive at 



