Value of 

 localising wells 



MOSQUITO WORK IN KHARTOUM, ETC. 29 



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 weU in Khartoum, a matter of great importance in the event of any 

 extensive outbreak of cholera or enteric fever. The original number of wells sent 

 me by the Mudir, and obtained fi'om information fui'nished by the local sheiks, 

 fell far short of the actual count. 



Certain water insects which prey on the larvffi have been found, but none are 

 so voracious as to yield hopes that they may be turned to practical account. 



More may possibly be exjDected fi-om the discovery in the United States of a new 

 sporozoon parasite' of the Anophelina, and of a larval round worm, Againoineriiiis 

 culicis (Stiles)'" which is said to render the female mosquito barren and induce Parasites of 



^ ' -*■ the mosquito 



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 

 apphcation, easily soluble, readily diffusible, not obnoxious to the eyes or nose 

 and at the same time cheap. The nearest approach to this is a weU-kno'svn 

 proprietary preparation made fi'om anilin dyes and used successfully in the case of 

 rice fields. 



Having at one time found that chrysoidine, the hydrochloride of di-amido-azo- 

 benzene (C12 H,, N4 HCl), a yeUow anilin colour, was most deadly to fish in very 

 dilute solutions, it seemed worth while to experiment with it upon larvaj and pupag. 

 It was found that a solution of 1 in 30,000 was efficient both as regards Anopheles 

 and Culex larvae, the foi'nier being the less resistant. The amount, however, 

 required for pi'actical purposes would be too expensive, and the solution has Action of 



,1 . 1, 1 chrysoidine, an 



rather a strong yellow colour. aniiin dye 



The following are the details of the few experiments performed. As far as 



possible the water in which the larvaj and pupae were found was employed : — 



No. Strength of Solution. Eesult. Temp, of Water. 



1 1 in 1,000,000 Some advanced larvaj of Culex fatigaiis 28-5°C 



dead within 72 hours. Pupte formed 

 and hatched out. Some alive after 4 

 days. AU dead in 5 days. 



2 1 in 100,000 Half the larva3 of Cidex fatigans dead Do. 



within 48 hours. Several living after 

 72 hours. 



3 1 in 75,000 Some larvaj of Culex fatigans alive after Do. 



72 hours. Discontinued. 



4 1 in 50,000 Half the larvaj (young) dead in 24 hours. Do. 



not in 10 hours. AU dead -within 31 

 hours. 

 5a 1 in 50,000 KiUed the larv® of Pyretophonif! costalis Do. 



within 24 hours, but not those of 

 Culex fatigans. 



' Johnson. Journal of Medical Research. Vol. yii., 1902. No. 2, p. 213. '' Lancet, 1/8/03 



