250 ZOOLOGY FOR MEDICAL STUDENTS chap. 



of guarding against the bites of infective mosquitos. In regions where 

 mosquitos are abundant it is quite impossible when leading an ordinary- 

 out-of-door life to avoid altogether being bitten. But it should be 

 remembered that only a small proportion of mosquitos are infective and 

 consequently any reduction in the number of bites means a reduction in 

 the chance of infection. The hours of sleep should be passed in the 

 shelter of an efficient mosquito net, properly used, and for persons on 

 night duty in the midst of swamps it is worth while to smear the exposed 

 parts of the skin with some oil repellent to mosquitos and other biting 

 insects ^ although such mixtures are themselves apt to cause much 

 irritation to persons with delicate skins. In the case of regions where 

 malaria is not of normal occurrence the immigration of numerous malarial 

 patients makes it of importance to take measures to reduce the chance 

 of their infecting the local mosquitos. Such patients should be prevented 

 so far as possible from settling in fen lands and other low-lying districts 

 where mosquitos are more numerous than elsewhere, and patients actually 

 in such districts should during their attacks be kept in the seclusion of 

 mosquito nets or gauze-screened rooms. 



Stegomyia, the genus concerned in the spread of Yellow Fever and 

 Dengue Fever, is controlled by the methods already mentioned, but it 

 should be remembered that mosquitos of this genus are particularly 

 prone (i) to breed in water-butts, old tins and other receptacles, and 

 (2) to haunt the interior of houses and ships. In the latter case they 

 are best cleared out by fumigation,^ care being taken to paper up all 

 chinks, to leave the room or cabin sealed up for three hours, and to burn 

 the apparently dead mosquitos. 



The Chironomidae include a large variety of Midges. The genus 

 Ckironomus, one of the commonest, has a worm-like aquatic larva which 

 in some species is coloured red by haemoglobin (" Blood-worms "). In 

 the genus Culicoides or Ceratopogon the female is blood-sucking and is 

 in fact the commonest type of blood-sucking midge or " sand-fly." In 

 some regions these midges are even more annoying than mosquitos, for 

 owing to their small size ordinary wide-meshed mosquito-nets are no 

 protection against them, and owing to their occurring in swarms, not 

 every night but only occasionally, immunity to their poison is not 

 developed so readily as in the case of mosquitos. 



1 E.g. Oil of Cassia i part, Red Oil of Camphor 2 parts, Lanoline or 

 Vaseline or Salad Oil 4-5 parts (Hewlett). 



" One pound of sulphur per thousand cubic feet of room. Burn in an iron 

 pan moistened with spirit. 



