57 



entered a ]>rook. The spriiiu- avus free from larva . l)ut the drain teemed 

 Avith them throughout its entire length. Over this drain kcn-osene oil 

 was sprinkled by means of a watering pot. About 4 gallons sutiiced to 

 cover the drain thickly with oil. "The larvicidal eflf'ect was imme- 

 diate, and on the following day no living larvte were seen. Four days 

 later traces of oil were still present in places. Eight days later small 

 iarva> were present along th(^ whole drain. * '^ " A weekly appli- 

 cation of paraffin then would efi'ectually prevent the formation of the 

 perfect insect in these situations." 



The rapid disappearance of the kerosene covering in this last experi- 

 ment is quite contrary to the results of our applications made to still 

 pools of water. This may have ])eeu due in part to the fact that there 

 was more or less of a current in the drain, and may also have been 

 due to the use of an especially volatile kerosene. The writer is now 

 advising the use of the grade known as lubricating- oil as the result of 

 the extensive experiments made on Staten Island. It is much more 

 persistent than the ordinary illuminating oils. 



An interesting plan, suggested to the writer by Mr. W. C. Kerr, 

 of New York, in conversation, to disseminate oil over salt marshes, 

 was that of putting barrels of oil in the marshes in winter when the 

 ground is frozen and piercing the barrels with small holes so that the 

 oil will escape slowly through the following breeding season. The best 

 method of distributing oil on the surface of water is a practical ques- 

 tion which each experimenter is apt to settle for himself. The writer 

 has adopted the plan of simply pouring the requisite quantity of oil 

 upon the water and allowing it to spread by itself, which it does in the 

 course of time. The Staten Island and Summit, N. J. , people use a 

 spray pump, but in some ways this seems to the writer not perfectly 

 satisfactor3^ A great deal of kerosene is apt to be wasted and the 

 continuous layer of oil which is desirable is frequently not brought 

 about. The Liverpool School of Tropical Diseases advises as the 

 result of the Sierra Leone work that the oil can be best applied by 

 smearing the pool with a rag fixed to the end of a stick and dipped in 

 a pot of oil. " In this manner a number of pools can be dealt with in 

 live minutes at the expense of very little oiL" 



OTHER LARVIGIDES. 



Permanganate of^^otash. — Other substances have been experimented 

 with. Two years ago many newspapers contained an item concerjiing 

 the use of permanganate of potash. As this item was credited to the 

 Public Health Journal it gained a great deal of creden(?e, and was 

 afterwards mentioned in an interesting article by Mr. A. C. Weeks, 

 in the Scientific American. The published note 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 



