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to, says: ‘‘On the whole, the most promising method which suggests 
itself is the employment of some cheap solid material or powder which 
dissolves slowly, which kills the larve without injuring higher animals, 
and which renders small pools uninhabitable for the larve for some 
months. If, for instance, a cartload of such material would suffice 
to extirpate the larve over a square mile of a malarious town, the 
result would be a large gain toits healthfulness. Dr. Fielding-Ould 
has lately reported favorably on tar.” 
Tar and its compounds.—Again, in the report of the Liverpool 
School of Tropical Diseases the following words occur: ‘‘ Perhaps more 
permanent oil than kerosene would be more permanently effective. 
Fresh tar dropped in a puddle makes a film like that of oil and has 
been favorably reported on. Quicklime has been suggested, and all 
these should certainly be tried.” 
The writer is rather at a loss to know exactly what is meant by the 
expressions ‘‘fresh tar” and ‘‘tar” in the above paragraphs. He has 
conducted an experiment, however, with a substance known to the 
trade as ‘‘ coal tar,” a thick viscid liquid. A few large drops of this 
substance were dropped into a glass vessel containing approximately 
2 quarts of water in which were more than 100 full-grown larve of 
Culex. All the drops but one sank at once to the bottom, the last one 
floating upon the surface for some time. No surface film seemed to 
form from the tar, but after the expiration of forty-eight hours the 
water was found to be more or less impregnated by the tar, having 
turned somewhat darker in color, while the odor of the tar was per- 
ceptible. At the expiration of five days nearly all the Culex larve 
were dead; 1 had succeeded in transforming to pupa, and 5 or 6 remained 
at the surface enfeebled and dying. Thus more than 95 per cent had 
been killed. In the meantime, however, twenty-four hours after the 
experiment began, 3 egg masses were laid on the surface of the water 
by outside females of Culex. These had hatched in forty-eight hours 
more, and on the fifth day, although the original full-grown larve 
were practically exterminated, many young larve were swarming 
actively about in the tar water. They continued to grow and to 
remain apparently perfectly active and healthy, although the odor of 
the tar was distinctly perceptible and the color of the water was dark, 
and even a thin oily film remained over a portion of the surface. 
From this experiment it was plain that the killing effect of the tar 
in the preparation used is comparatively fugitive, and it was next 
decided to test some of the coal-tar products. The object of this line 
of experimentation was not only to test the suggestions of the English 
observers, but also on account of the fact that as almost every com- 
munity manufactures its own illuminating gas it was considered an 
easy and probably econominal way of securing a mosquito larvicide, if 
it should prove to be effective. Coal tar is distilled into various grades 
