SEA-WATER POOLS AND MALARIA 225 
Continuing his researches at Samarang, de Vogel found other pools of water 
inhabited by Anopheles larve, 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 
swarms with Anopheles larve, while Culex larve 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 larve 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 larve 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 larve 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 larve 
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 hemoglobinuria 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 larve in check, while in the now isolated pools 
the Anopheles larve can develop unhindered. 
