224 MOSQUITOES OF NOKTH AMERICA 



season, when all other breeding-places, artificial and natural, have ceased to 

 exist." 



ANOPHELES BREEDING IN SEA- WATER. 



We have mentioned above a statement by Smith that Anopheles has been 

 found in the salt marshes, and this observation has been repeated by others. 

 Anopheles have been found breeding in salt or brackish water in many parts of 

 the world ; in every case the habit has been found restricted to certain species. 

 An article was published by Dr. W. T. de Vogel, health officer of Samarang, 

 Java, in the Atti della Societa per gli Studi della Malaria for 1907, bearing 

 upon upon this question, and his observations are so important that we devote 

 considerable attention to them. De Vogel found that the investigations of 

 several Italian workers have negatived the idea that Anopheles can multiply in 

 pure sea-water and that they have shown that the maximum proportion of 

 sodium chloride in the water which Anopheles larvas can stand is 1.87 per cent 

 according to Perrone, and 1.75 per cent according to Vivante. De Vogel, 

 having made some elaborate studies in regard to malaria at Samarang, found 

 as early as 1902 that Anopheles was breeding in a certain pool containing 2.8 

 per cent of chloride of sodium. Later he verified these results in several in- 

 teresting cases. One of these was the island of Onrust, a small coral island 

 situated two thousand meters from the mainland, and which contains no fresh 

 water whatever. The distance from the mainland is such that even if Anopheles 

 were brought from the mainland by winds they would not be numerous enough 

 to cause trouble. Nevertheless a marine station established on the island had 

 to be abandoned on account of the ravages of malaria among the workmen and 

 Dr. de Vogel believed that this was due to Anopheles breeding in the sea-water 

 i;pon the island itself. 



De Vogel studied also the conditions in the Karimon Islands, a little archi- 

 pelago in the Java Sea, sixty-five kilometers from the coast. The first colonists 

 in this archipelago were convicts and were sent there to cut down the forests of 

 rhizopores. There were no buildings, and the convicts Avere forced to sleep on 

 the earth. The mortality was between two and three thousand in two years. 

 Later one of the officers named von Michalofski — a plain man but full of good 

 sense — succeeded in putting a stop to the excessive mortality by drying the sea- 

 water pools, removing a part of the forest, and raising the ground on which the 

 men slept. The success which followed these measures leads de Vogel to sup- 

 pose that the mortality had been caused by malaria, and this supposition is all 

 the more probable since, as he himself has verified, malaria is today rife among 

 the population of the islands. 



There is on the island of Grand Marimon only a single permanent source of 

 fresh water which has only one restricted outlet. During the dry season there is 

 no mingling of fresh water with sea-water, so there exist during that season 

 many pools of dead sea-water peopled with Anopheles larvie; these pools contain 

 not less than three per cent of sodium chloride and must then be considered as 

 concentrated sea-water. 



