57 
entered a brook. The spring was free from larvee, but the drain teemed 
with them throughout its entire length. Over this drain kerosene oil 
was sprinkled by means of a watering pot. About 4 gallons sufficed to 
cover the drain thickly with oil. ‘‘The larvicidal effect was imme- 
diate, and on the following day no living larvee were seen. Four days 
later traces of oil were still present in places. Hight days later small 
larve were present along the whole drain. * * * A weekly appli- 
cation of paraffin then would effectually 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 been 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 
satisfactory. 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 
five minutes at the expense of very little oil.” 
OTHER LARVICIDES. 
Permanganate of potash.—Other substances have been experimented 
with. ‘Two years ago many newspapers contained an item concerning 
the use of permanganate of potash. As this item was credited to the 
Public Health Journal it gained a great deal of credence, 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 
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