SEA-WATER POOLS AND MALARIA 225 



Continuing his researches at Samarang, de Vogel found other pools of water 

 inhabited by Anopheles larvae, in proximity to the sea. One of these places had 

 a surface of 20 to 30 square meters and a depth of from 10 to 30 centimeters. 

 It was connected with a pool of sea-water by a bamboo-pipe crossing the dike. 

 The pool is thus invaded by seaweeds, but the fish can not enter. This place 

 Bwarms with Anopheles larva, while Culex larvae are not found there. In this 

 pool the percentage of sodium chloride is about 2.88, while in the water of the 

 neighboring swamps it varies between 2.44 and 2.76. 



Other instances of the occurrence of Anopheles larvae in concentrated sea- 

 water are given with careful descriptions and the author finally draws the fol- 

 lowing conclusions : 



*' 1. There are species of Anopheles which can live very well in sea-water. 



" 2. These mosquitoes lay eggs which develop even in sea- water which has been 

 evaporated to half its original quantity. 



" 3. These larva in the gradually evaporating pools of sea-water can stand an 

 evaporation of the water to one-third of its bulk, but do not appear to transform 

 to adults if the concentration be greater than this. 



" 4. The larvae coming from eggs laid in sea-water of high concentration can 

 accomplish their entire metamorphoses in almost the normal time. This is true 

 even when the water has such concentration that the development of larvae 

 originally hatching in unconcentrated sea-water would be retarded by this salt 

 water." 



In the opinion of de Vogel the bad reputation which the coral islands of the 

 East Indies have, is explained by his observations, since so many cases of malaria 

 are observed along the coast during the dry season when all the rivers and fresh- 

 water streams are dried up. Villages near the sea, in the middle of tidal pools, 

 have had during a period of ten years an average mortality of from 1 to 4 per 

 cent each year. In villages further away from the sea, where the ponds have 

 been abandoned or neglected and the sea-water, therefore, is isolated, there is a 

 mortality which varies from 8 to 10 per cent each year. The pools in these 

 regions during the dry season have a proportion of sea salt equal to that of the 

 ocean. In this dry season the death rate is greatest, and this is exclusively due 

 to the Anopheles breeding in the sea-water ponds. 



" The great mortality is surely due to malaria, since almost without exception 

 the cases of pernicious malaria or haemoglobinuria which are treated at Sama- 

 rang come from the south border of tidal pools. A quarter of Samarang called 

 Zeestrand was inhabited by well-to-do citizens of the city who had good health, 

 although surrounded by pools. Then, when on account of the banking of the 

 coast, these pools were left further from the sea, the locality became unhealthy 

 and the inhabitants were forced to quit the quarter because the death rate from 

 malaria reached terrible proportions. The empty houses of this quarter still 

 bear witness to past grandeur. The mortality of the indigenous population 

 which still remains there has been on the average during the last ten years 9.7 

 per cent per year." 



The difference in the malarial rate is not due to any change in the character 

 of the water itself. When the pools were tide-water pools fish and other life 

 had access and kept the mosquito larvae in check, while in the now isolated pools 

 the Anopheles larvae can develop unhindered. 



