5 8 MALARIA 



algae or soap and alkali in the water. This can be 

 remedied by the addition of copper sulphate previous 

 to oiling. 



Tobacco Decoctions. — The writer has thoroughly 

 tested the efficiency of tobacco decoction, both in 

 the laboratory and in the field, and has found it 

 very effective, but the expense is prohibitive when 

 used on a large scale. Sulphate of nicotine (black 

 leaf 40), made by the Kentucky Tobacco Product 

 Company, was found to effectively destroy all wrig- 

 glers and tumblers when used in the ratio of 1 part 

 to 750 parts of water. Greater dilution proved un- 

 certain for the pupae, but 1 to 1000 is still effective 

 for the larvae. In field work this material was used 

 for smaller pools and experimentally on a good- 

 sized quarry hole pond effectively, but proved too 

 expensive. Ordinary "black leaf" tobacco decoction 

 cannot be used successfully in a greater dilution 

 than 1 part to 20 of water. It must be remembered 

 in all cases that a material in weaker strengths would 

 be just as useful and less expensive, provided it killed 

 the insect, even after a day or two, and this factor was 

 borne in mind during the progress of experimentation. 



Larvicide. — A larvicide generally used in the Panama 

 Canal Zone is prepared from crude carbolic acid. Its 

 manufacture and method of application are fully de- 

 scribed in an article by G. T. Darling in the American 

 Journal of Public Health for February, 191 2. From 

 this the following is quoted : — 



