97 



proportion of the larvas. I have several times tried the oil on road 

 and open meadow pools when there was onl}" a light wind blowing, to 

 find in a few minutes all the oil film at one side and a very fair con- 

 gregation of larvse at the other. In grassy pools the tendency is for 

 the oil to gather about the vegetation, and where there is much floating 

 matter the spread of the oil is materially hindered if not altogether 

 prevented. 



Admitting, then, the very great i-ange of usefulness of the petrole- 

 ums, it was deemed useful to make a number of laboratory trials of 

 other substances to determine whether it would not be possible to 

 obtain something that would mix readily with the water, making it 

 unfit for wrigglers to live in for some considerable period. 



Materials for experimental purposes were sent in l)y the Phinotas 

 Chemical Company of New York; Mr. F. B. Kilmer, president of the 

 New Brunswick board of health, sent me a supply of chloro-naj^hthalum 

 from the stock of the board, a series of other cresol preparations, and 

 a variety of disinfectants from Johnson & Johnson. These latter 

 samples were not of the firm's manufacture, but, rather, from the stock 

 carried for general use. Other things were purchased as needed. 



The larvae and pupse used for the experiments were usually obtained 

 from a series of pails kept partly filled with water in my garden, but 

 some were obtained from out-door pools within the city limits. The 

 species was always pimgetis, with an occasional small admixture of 

 terrltans or restuans^ until in August Anojplieles punctipennin became 

 common enough to be added. 



PERMANGANATE OF POTASH. 



Sk 1-quart jars were used, each containing 16 ounces of water, in 

 which were from 50 to 100 larvte, ranging from one-fourth to full 

 grown. A stock solution of permanganate was made, of which 8 drops 

 equaled 1 grain of the cr3^stals. 



Jar No. 1 received 1 grain; jar No. 2 received 2 grains; jar No. 3, 

 4 grains; jar No. 4, 8 grains; jar No. 5, 16 grains, and jar No. 6,32 

 grains of permanganate. 



In each case the water became at once distinctly discolored, and 

 where the larger amounts were used became so deeply purplish that 

 the liquid was opaque and the wrigglers could not be seen except at 

 the surface. No immediate efl'ects were observable in any jar. 



After forty-eight hours all the larva^ in jar No. 1 were yet alive and 

 active. In jar No. 2 about 20 per cent of the larvje were alive, and 

 these were the larger specimens that would have pupated shortly. In 

 the jars containing tlie stronger mixtures all the hirva3 were dead, and 

 it is fair to say that for certain death to the larva in a reasonabk; time 

 at least 4 grains of permanganate would be required in every pint 



221Y0— 03 7 



