Page:The Indian Medical Gazette1904.pdf/32

 exception of one small puddle under a tree which contained anopheles, I liave not been able to find any larvse for some distance around, but I hope that those more unfortunate who have pools with anopheles in them might repeat my experi- ment. I hope later to send you a method by which, if I may use the phrase, larvae can by artificial means be desiccated. I am now working on this. I find that a shallow brick tank with the usual mud and leaves at the bottom, tlie tank being in the sun, is the best place to take the mud from. The mud when quite dry is scraped up and put into a card-board box. A small glass vase in which water has been placed is best. I take some of the dry mud and drop it on the water, this floats at first and then gradu- ally drops to the bottom ; from two to eight hours after, according to the temperature of the water, the larvse can be seen swimming about. I find at Bareilly that tanks and certain shallow puddles contain water up to the beginning of April, during which time culex can be found. Larvse, nymphse and eggs are to be found in these tanks and pud- dles, but from April to the middle of June, or till the rains break, mosquitoes are not seen. There are no tanks or puddles, water being taken from wells. It is this period which mosquitoes have to tide over. In my experiment on eggs in April 1901 I found larvse in the mud, though this is open to doubt, viz., that they may have been introduced into the glass vessel from water taken from my tub, but from recent experiments I believe myself they were in the dry mud. My experiments, as far as I am aware, were carefully carried out, and errors guarded against; so it can be taken that larvse of culex can survive three months complete desiccation. This would easily tide over the period of April, May, and June in Bareilly, when water on the surface is very scarce, and I have no doubt that the period of desicca- tion can be considerably prolonged and the larvae survive.

I believe this is the only method by which culex tide over periods inimical to their breeding. I have kept mosquitoes, and have tried various methods to prolong their lives ; but 20 to 30 days is the longest I have been able to keep them alive, without food or water eight days. Now during the hot weather, at least in Bareilly, viz., April, May and June, a mosquito is very rare, in fact I have not seen one. If they are present, what do they live on ? Green vegetation is scarce, at least what one would expect a mo'-quito to eat. How can they then survive the three months in which water and food, I might n^y, are absent? I am still working at experiments to find if it is possible to keep a mosquito alive without food or water. I find if kept in the dark, they live longer than if exposed to light. It may be that mosquitoes breed in April, may have the power of hibernating, and doing without food or water; if not, I do not see how they can s\nvive, especially in the Punjaub, where food, except animal, is more scarce than in the Upper

Provinces. If they prolonged their lives on animal food, why are they not seen and felt ? Eight days is the longest period I have been able to keep a mosquito alive without food or water. Under favourable conditions, from twenty to thirty da3's. In Bareilly I have found culex in all months except April, May and June, and it is during these months, when food for the mos- quitoes, and water for eggs, larvae, and nymphae is absent, that the power of the larvae of a certain age to survive dessi cation enables them to tide over the period during which they would become extinct.

Table giving date in which dry mud was put into water, with number of hours after which larvae appeared, their apparent age ; date on which nymphcB and mosquito appeared.

They breed usuall}' in stagnant pools contain- ing vegetable dcibris, such as hollows in trunks (»f trees. This species wonders further from its breeding places than culex does, and is often found where there is no possible breeding place and where C. Fatigans disappear.

Only one variety of anopheles is known here, the A. Rossii, and that has been found only in two places. The breeding-place they affected was a series of borrow pits excavated during the building of a convict barmck. This variety was also disccwered at Dundas Point. Except when these borrow pits were in existence, it was impossible to find any anopheles larvjB^on Ross