REMEDIES AGAINST MOSQUITOES 195 



it dangerous to use as an application to ponds. The 

 pyretlirum powders are exjDensive and not thoroughly 

 effective. 



The use of tar was suggested by Dr. Fielding-Ould, of 

 the Eng-lish West African Commission, and creosote oil 

 has been suggested as a probable larvicide of value. Ex- 

 periments made by the writer in the summer of 1900 Avith 

 coal tar showed that this substance is slow in its action, 

 not perfectly effective, and not at all persistent. Experi- 

 ments with the two grades of creosote oils (by-products 

 in the manufacture of illuminating g-as) indicated that 

 they destroy the larvae, but not nearly so rapidly as the 

 various grades of kerosene. It is possible that the creo- 

 sote oils may prove to be more permanent than the 

 lighter illuminating oils, though they are not as rapid in 

 their effect and not as satisfactory, on the whole, as the 

 grade known as fuel oil. 



A great deal has been said about the value of perman- 

 ganate of potash as a larvicide for mosquitoes. In the 

 summer of 1898 a paragraph was copied in nearly all of 

 the newspapers of the country, which was attributed to 

 the Pahllc Health Journal, and which read as follows: 



Two and one-half hours are required for a mosquito to develop 

 from its first stage, a speck resembling cholera bacteria, to its 

 active and venomous maturity. The insect in all its phases may 

 be instantly killed by contact with minute quantities of perman- 

 ganate of potash. It is claimed that one part of this substance in 

 1,500 of solution distributed in mosquito marshes will render the 

 development of larv* impossible ; that a handful of permangan- 

 ate will oxidize a ten-acre swamp, kill its embryo insects, and keep 



