DESTRUCTION OF LARV^. 73 



mals. What a boon it would be if we could keep the surface of a whole pond free from 

 larvae simply by scattering a cheap powder over it, once in six months or so. It is 

 very possible that such a substance exists, but unfortunately we have not yet discov- 

 ered it a 



A great many experiments have been tried with poisonous sub- 

 stances in the search for the desideratum described by Doctor Ross, 

 but although it is now seven years since he wrote this paragraph we 

 still have failed to discover it. As early as 1899 Celli and Casagrandi 

 published an account of an elaborate series of laboratory experiments 

 on the destruction of mosquitoes by various chemicals in a paper enti- 

 tled '^La Distruzione delli Zanzare," published in the Annali d'Igiene 

 Sperimentale. These experiments resulted in little practical good, 

 and practically the best of all the larvicides, namely, the petroleum 

 products, were discredited by the authors in question. 



In the last few years many substances have been experimented 

 with, both in the United States and in other parts of the world, and 

 there has been from time to time a newspaper notice, or a series of 

 newspaper notices, of some new substance which careful experimen- 

 tation has shown to be of little or no service. In this way the use 

 of permanganate of potash received much advertising in 1900, but 

 as the writer has elsewhere pointed out, as a result of careful experi- 

 mentation it was found that small amounts of the chemical have no 

 effect whatever upon mosquito larvae, which were, however, killed 

 by using amounts so large that instead of using a handful to a 10-acre 

 swamp, as had been stated in the newspapers, at least a wagon load 

 would have to be used to accomplish any result; moreover, twenty- 

 four hours after the use of this large amount and after the larvae were 

 killed, the same water sustained freshly-hatched mosquito larvae per- 

 fectly, so that even were a person to go to the prohibitive expense 

 of killing mosquito larvae in the swamp with permanganate of potash 

 the same task would have to be done over again two days later. 



In 1904 a publication by the Bureau of Plant Industry of the United 

 States Department of Agriculture, on the use of sulphate of copper 

 against algae and other microscopic plant-life, put certain newspaper 

 men on the wrong track, and a number of articles were published 

 making the erroneous statement that the Department of Agriculture 

 recommended sulphate of copper as a perfect remedy against mos- 

 quito larvae. So widely was this alleged discovery heralded that 

 careful experiments were at once made in the Bureau of Entomology, 

 by Dr. John B. Smith, of New Jersey, by Dr. W. E. Britton, of Con- 

 necticut, and by other entomologists, with the result that the substance 

 was found to be of very slight value as a larvicide, and of really no 

 practical value whatever. 



Several proprietary mixtures or mosquito compounds have been 

 prepared and placed on sale for the purpose of destroying mosquito 



"Mosquito Brigades, London, 1902, pp. 33-34. 



