THE MOSQUITO 



1139 



occurrence in the tropics, and, possibly, this is also the reason of 

 the rarity of P. malarice in the low country of the tropics, while its 

 presence in the hills is common. 



Here may also lie the explanation of the universal distribution 

 of P. vivax in both the tropics and temperate zone; for Jancso's 

 researches show that it can develop through a wide range of tem- 

 peratures. 



But these are not the only factors concerning the AnopheHnae and malaria, 

 for Schaudinn showed that the mosquito eggs may possibly be infected by 

 the malarial parasites, and this at once raises the question whether they cannot 

 be carried via eggs, larvae, and pupas into a second generation of mosquitoes. 

 If so, this would explain some outbreaks of malaria, but so far Schaudinn's 

 work has not been confirmed. 



Another point of importance is the fact that when new lands are 

 opened, it is asserted that people suffer more severely from malaria 

 than can be explained by any theory brought forward at present. 

 For example, it is stated that if a zone of forest on a steep hillside 

 be burnt in the dry season, and then cleared by coolies, who return 

 every night to the quarters where the other estate coolies also sleep, 

 these clearing coolies will suffer severely from malaria, while their 

 fellows v/orking on other portions of the estate will be but little 

 affected. The explanation of this is not that emanations have 

 arisen from the soil and invaded the bodies of the coolies — indeed, 

 after the description of the life-history of the malarial parasite 

 already given, this would be a reductio ad absurdum — but merely 

 that the exposure to the sun or the harder work has lowered the 

 vitality of these coolies, and has given the germs already in their 

 system a chance to develop. 



It has also long been thought that the mechanical opening of new 

 ground by digging produced the disease, but Ross has pointed out 

 that in Mauritius the digging of earth for years caused no malaria, 

 until some new factor was introduced which occurred in the sixties 

 of last century; this factor we now know to have been the introduc- 

 tion oiPyretopihorus costalis into the island. 



When an attack of malarial fever occurs in a person living in a 

 place where there are no Anophelinae, it is the result of infection 

 obtained in some other place where these mosquitoes are to be 

 found. 



It may safely be concluded that, as far as our present knowledge 

 goes, certain of the Anophelinse are the only carriers of malaria, and 

 upon this public prophylaxis must be based. 



A female mosquito, apparently, can live for at least a month 

 (Ross), if not longer. This does not include such dormant periods 

 of its life as the hibernation in the cold or aestivation in dry seasons, 

 when it may live for a long time in damp places. 



The eggs of the Anophelinse are laid only in natural collections 

 of water supplied with water-plants, such as the back eddies of 

 streams, close under the banks, which are especially good breeding- 

 places. The young imagines, apparently, do not usually travel, 



