3
which rain-water collected. Some days later, I noticed very large numbers
of larvae of A. stephensi and Stegomyia fasciata breeding in it. Some of
the larvae and pupae were collected and no less than 68 adult A. stephensi were
bred out in the course of three days. This observation gives an indication
as to the numbers a small breeding place of this kind may produce during a
single season.
It will be remembered that in Bombay, A. stephensi, which is a domestic
mosquito, breeds profusely in wells, cisterns, and garden-tubs. In Calcutta,
fortunately, there are practically no wells. The wells formerly existing have
been mostly replaced by the cisterns, which are present possibly in larger
numbers even than those in Bombay. For example, in a certain moderately
populated part of Dharamtola Street, an area a little over 4/9 ths of a square
furlong in extent, had about 36 cisterns. This gives a rough idea of the
number of cisterns existing in Central Calcutta, which is nearly 3 1/2 by 1 1/2 miles.
The infection of cisterns by A. stephensi, although most obvious in Central
Calcutta, is not confined to this part of the city, as there are localities south
of Park Street and east of Circular Road where similar conditions exist. The
majority of the cisterns examined are found to be defective for one or more
of the following reasons:—(1) badly fitting or absent lids, (2) holes in the
top or sides of the cistern and (3) presence of a tube to allow surplus water to
overflow. All these defects allow mosquitoes to enter and lay their eggs
within the cisterns. The cisterns examined in various parts of Calcutta give
a varying percentage of infection with A. stephensi:—Amherst Street,
12 per cent., Shambazar 12.5 per cent., Nebutolla Street, 26.5 per cent., Bagh-
bazar 32 per cent., Strand Road (Nimtolla) 31 per cent., Nimtolla Ghat
Street 41 per cent., Nimtolla Street 35.5 per cent., Dharamtola Street,
(Central) 50 per cent., Bow Bazar Street 43 per cent., Machua Bazar Street
57 per cent., Cross Avenue Road 62 per cent., Chorebagan 50 per cent., Corn-
wallis Street 60 per cent., Jhamapukur 66 per cent., Clive Street 62 per cent.,
Canning Street 54.5 per cent., "Wood Street 31 per cent. (Vide Appendix.)
The respective percentages have been marked in the accompanying map.
It is not claimed that these figures are complete, as only portions of the city
were examined; but a sufficient number of cisterns have been examined in the
various localities mentioned to show the seriousness of the condition. The
survey of the cisterns was by no means easy. The chief obstacle was the sus-
piciousness of the house-owners who, anticipating some trouble, often refuse
to allow us to enter their houses. The lack of the necessary leisure and the
want of assistance prevented my making the survey as complete as I could wish.
But a beginning has been made and it is to be hoped that better facilities will
be given to complete the work in future. In any case the figures noted show
to what an extent the city of Calcutta has already been invaded by A. ste-
hensi, and the point to the need both for active measures of prevention as well
as for further investigation.
Measures suggested.—The prevalence of A. stephensi in Calcutta
reminds one of the conditions existing in Bombay which eventually led to an
outbreak of epidemic malaria in 1907 and 1908 unprecedented in the history
of that city. In Bombay the chief breeding places of A. stephensi were the
open wells, cisterns and tubs.* In Dhobi Talao and in the north Fort area
there were on the average nearly four wells per acre. But in Calcutta, in
many parts, there are 7 cisterns for every acre and in some parts more; and
in some cases, over 60 per cent. of these cisterns are breeding A. Stephensv.
Thus we see that the condition of things in Calcutta is serious, threatening
as it does the health of the city and exposing the population to the risk of
epidemic malaria, just as in the case of Bombay.
While people in the central parts of Calcutta are exposed to the attacks
of A. stephensi, those in the suburbs have to meet in addition the onslaughts
of other malaria carriers, such as A. fuliginosus, listoni and sinensis. No
wonder, therefore, Calcutta is never free from malaria. The apparent free-
dom of the city from epidemic malaria is probably due to the fact that the
ratio of dangerous anopheles to the population is still relatively low, and it
is only in certain localities that it exceeds the " malaria point." The number
* C. A. Bentley. Malaria in Bombay, 1911, Government Central Press, Bombay.