1900.] and the distribution of Anopheles Mosquitos. 473 



evidence that the health of this tract has been influenced by the railway 

 or the Grand Trunk Road, and the spleen variations cannot possibly be 

 attributed to their action. 



Distribution of the Anopheles Mosquitos. 



It must now be taken as proved that malaria can be communicated 

 to man by the bites of the Anopheles genus of mosquitos, which have 

 previously bitten another case of malaria, and in whose body the 

 Plasmodium has undergone developemental changes. It still, however, 

 remains to be proved that this is the only or even the most common 

 way in which the disease is obtained, and it is worthy of note that 

 Laveran, who was the first modern exponent of the mosquito theory, is 

 still of the opinion that it will not explain all that is known of the 

 etiology of the disease. Still enough is known to make it highly advisable 

 to consider the question of the possibility of destroying the particular 

 breed of mosquito which plays a part in distributing malaria. This 

 should not be impossible in limited areas, at any rate, if Major Ross's 

 statement as to their breeding-grounds is correct, namely, that they 

 mainly breed in small pools which are not inhabited by fish, and yet are 

 not so small that they will dry up in a few days, and consequently that 

 such suitable pools are few and far between. In order to test this 

 statement I searched for the larvae in several Municipalities, but regret 

 to say that I have not been able to confirm Ross's statements. On the 

 contrary, I found the Anopheles larva3 in numerous tanks as well as in 

 the small pools which Ross describes, and that too in spite of the former 

 as well as some of the latter abounding in fish. This having been 

 ascertained, a small portion of Maniktolla, measuring about one-sixteenth 

 of a square mile, and containing some thirty tanks, was further examined. 

 During the dry months of from February to May, which are the 

 minimum fever months of the year, I found the Anopheles larvae in 

 from one-third to two-thirds of these tanks, often in enormous numbers, 

 one of them for example, having been estimated to have contained 

 several million larvae on one day on which it was examined in May. In 

 the earlier months especially they were also found in several small 

 pools, but the numbers there were nothing as compared to those in the 

 tanks, which are certainly the common breeding-ground of the Anopheles 

 in the dry season at any rate. Three pools in a low-lying area are of 

 interest, for in one, some two yards square, and a second which was five 

 yards in diameter, fairly numerous Anopheles larvae were found in spite 

 of the presence of small fish in both, so that it is not surprising that they 

 can also survive in tanks which are swarming with fish. Further, I failed 

 to find any cases of fever near the infected tanks in the hot weather. As 

 J. ii. 62 



