MOSQUITO WORK IN KHARTOUM, ETC. 29

localising wells

White Nile. The pools so formed, were however shallow, soon dried up, and at no time were mosquitoes found breeding in them.

A point worth mentioning is that the labours of the brigade have served to locate every well in Khartoum, a matter of great importance in the event of any Value of extensive outbreak of cholera or enteric fever. The original number of wells sent me by the Mudir, and obtained from information furnished by the local sheiks, fell far short of the actual count.

Certain water insects which prey on the larva? have been found, but none are so voracious as to yield hopes that they may be turned to practical account.

More may possibly be expected from the discovery in the United States of a new sporozoon parasite1 of the Anophelina, and of a larval round worm, Agamomermis culicis (Stiles)2 which is said to render the female mosquito barren and induce Parasites of disease in the insect. As has often been said, what is wanted is a thoroughly good larvicide, non-volatile, harmless to vegetation, non-poisonous, simple in application, easily soluble, readily diffusible, not obnoxious to the eyes or nose and at the same time cheap. The nearest approach to this is a well-known proprietary preparation made from anilin dyes and used successfully in the case of rice fields.

Having at one time found that chrysoidirie, the hydrochloride of di-amido-azo- benzene (C12 H12 K4 HG1), a yellow anilin colour, was most deadly to fish in very dilute solutions, it seemed worth while to experiment with it upon larva? and pupae.' It was found that a solution of 1 in 30,000 was efficient both as regards Anopheles and Culex larvae, the former being the less resistant. The amount, however, required for practical purposes would be too expensive, and the solution has Action of rather a strong yellow colour. chrysoidine, an

J ' anilin dye the following are the details of the few experiments performed. As far as possible the water in which the larva? and pupa? were found was employed :—

No. Strength of Solution.

1 1 in 1,000,000

2 1 in 100,000

3 1 in 75,000

4 1 in 50,000

5a 1 in 50,000

Eesult. Temp, of Water. Some advanced larva? of Culex fatigans 28'5°C

dead within 72 hours. Pupa? formed and hatched out. Some alive after 4 days. All dead in 5 days. Half the larva? of Culex fatigans dead Do.

within 48 hours. Several living after

72 hours. Some larvae of Culex fatigans alive after Do.

72 hours. Discontinued. Half the larva? (young) dead in 24 hours, Do.

not in 10 hours. All dead within 31 hours. Killed the larva? of Pyretophorus costalis Do.

within 24 hours, but not those of

Culex fatigans.

1 Johnson. Journal of Medical Research. *‘Vol. vii., 1902. No. 2, p. 213. 2 Lancet, 1/8/03