TEE NATURAL EISTORY OF BOMBAY MALARIA. 409 



Some wells are not placed within the house but in a small yard at 

 the back or in the compound, but many of them are so arranged as 

 to be overlooked by windows specially made for the purpose of 

 drawing water. In the northern portion of the island wells are 

 usually in gardens or compounds and were once used largely for 

 irrigation purposes, being surrounded by pucca tanks and water 

 channels. Wells of this kind are generally very large and deep, 

 some being as much as 25 ft. in diameter and from 50 to 100 ft. 

 in depth. 



N. stevhensi has been found breeding in wells of every sort, but 

 the darker wells inside the houses generally appear to be the most 

 dangerous. They have been found in wells so shallow that it was 

 quite possible to see the bottom and in others with a depth of from 

 20 to 30 ft. of water ; they have also been found in wells where the 

 water was far below the surface of the ground quite as often as in 

 wells where the water was almost within reach of the curb ; they 

 often occur in wells containing much weed and floating matter but 

 not infrequently they are present in wells in which the water 

 appears absolutely clear. Wells in frequent use have often been 

 found to contain them in spite of statements to the contrary. 



Iron cisterns come next in importance to wells among permanent 

 breeding places of N. stephensi, and altogether some hundreds of 

 cisterns have been found to contain larvae of this anopheles. Some 

 of these cisterns are open ones but the majority are the usual 

 covered cisterns found all over the city. Very few cisterns of this 

 type are properly closed, and although they generally possess lids 

 or man-hole doors, the lids rarely fit, and the man-hole doors are 

 either left open or lost. During the monsoon I visited a very large 

 number of modern houses with terrace roofs, and in many cases I 

 found that nearly every cistern on the roof was breeding N. stejihensi. 

 This being so it is not surprising that residents in such houses 

 should frequently suffer from malaria, because among the native 

 servants who almost invariably live under the same roof, a certain 

 proportion are sure to harbour malarial infection and with malaria- 

 carrying mosquitoes breeding in the water-supply cisterns on the 

 premises, there is every chance for the spread of malaria among the 

 inmates. 



