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mutual friend Dr. D. C. Rees, lately Superintendent of the London School of Tropical Medicine, who put me in communication with Mr. Theobald. The insects which I have indicated by the letters, "n", "o", "p", "r", "r", and "s", I have carefully described, but not named. "p" may be Culex Fuscanus; the others are, I think, new species, but this question I shall remit to Mr. Theobald at the British Museum.
Culex Scutellaris is the black and white striped mosquito so common all over the Colony during the day time; Culex Fatigans and Culex Reesii are the equally common brown mosquitoes, to be found everywhere and at all seasons in the evening; Culex Obturbans is the very large dark mos- quito, also very widely prevalent. The others are less abundant, but for the most part occur pretty generally throughout the Colony.
It may be noted in passing that Culex Fatigans is the most usual intermediate host of the blood parasite, Filaria Nocturna, the cause of Elephantiasis and its kindred diseases, by no means uncommon in this locality.
While Anopheles as a rule only uses for breeding purposes clean water in more or less natural collections, the various species of Culex lay their eggs wherever stagnant water exists, in broken dishes, empty tins, flower pots, water tanks or barrels, drain traps, and the like. Nothing is too dirty to have its appropriate mosquito developing in it. Culex Obturbans is the most loathsome of all in its larval state, finding its most favourable conditions in decomposing urine.
12. I do not propose to enter here into details of prophylaxis against these insects, which I have dealt with in special reports; but in view of the approach of the cold season I desire to direct attention to observations which I made during last winter.
I was able to find the larva of Anopheles abundantly in the nullahs throughout the whole winter, in scarcely diminished numbers, though there were few in the pupa stage, and developinent at that season is evidently very slow or arrested.
I was able to note the effects of severe cold at the beginning of February. On 1st February, I had made a careful examination of the Kennedy Town nullah, and found Anopheles larvæ plentiful. On the 3rd there was a sudden rapid drop in the temperature, and when I examined the stream again on the 5th there were few larvæ to be seen. It seemed as if they had been killed by the cold. But fortunately I had some larvæ under observation at the time in a glass jar in my verandah. Under the influence of the cold these became torpid or sluggish, and most of them seemed dead. On the 7th, however, the sun shone out brightly, and the seemingly dead ones as well as the others became quite lively again. It is probable, therefore, that much of the diminution in numbers of the larva in the ravines during the winter is more apparent than real, since they are most easily recognised in ordinary circumstances, by their very characteristic movements when disturbed.
13. I mention this observation now in order that I may urge that efforts already being made by Government, and by owners of private property as well, to eradicate these pests should be redonbled during the coming winter months. New generations are during these months being developed either not at all, or at least very slowly, and therefore such efforts are certain to be very much more effective than during the summer. From experience in Hongkong, kerosene is at once the cheapest, safest, and most efficient larvicide.
I further urge upon householders in malarious parts of the city the desirability of making an effort to destroy as many as possible of the hibernating adult insects during the winter months, by occasionally fumigating with sulphur all servants' quarters, basements, boxrooms, stables, &c., where in ordinary circumstances the insects might remain undisturbed in dark corners for long periods.
I have the honour to be,
Sir,
Your obedient Servant,
Dr. J. M. ATKINSON,
Principal Civil Medical Officer,
$.,
Sr.
&r.
JOHN C. THOMSON, M.D., M.A.
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