t598 



THE FILARIASES 



again, this is very unequal, some of the islands — Barbados, for 

 example — being heavily infected, while in others, Grenada, the 

 infection does not appear to exist. 



The distribution must depend upon the presence or absence of 

 mosquitoes capable of disseminating the worm, but this aspect of 

 the epidemiology still requires a considerable amount of research; 

 further, the distribution of the suitable mosquitoes must depend 

 upon many factors concerning which we are quite ignorant. When 

 these conditions are better understood, the climatology will be 

 rendered more explicable. 



Two atmospheric conditions — viz., high air-temperature and con- 

 siderable atmospheric humidity — have long been known to be 

 associated with the prevalence of filariasis and elephantiasis, and 

 the reason of this has recently been explained by Fiilleborn's ex- 

 periments on Dirofilaria immitis. This observer found, as the result 

 of most careful experiments, that the Dirofilaria developed better in 

 mosquitoes if the air-temperature was high, and in that respect 

 resembled the malarial parasite; and, further, that at high tempera- 

 tures the DirofilaricB are able to leave the proboscis more easily, and 

 to penetrate the skin more quickly than at a low temperature. 



Further, the moisture in the air is of importance, as the Dirofilaria 

 passes from the proboscis on to the skin, and either makes its 

 own way through this into the tissues, or enters the aperture of 

 the mosquito's bite after it has withdrawn its stilettes, and, there- 

 fore, has to be for some time in contact with the skin, which, if dr}^ 

 will have a harmful effect upon it, but if moist, will not be injurious 

 to it. 



With reference to Fiji, Bahr concludes that it is possible that at 

 one time or another nearly every Fijian is the subject of filariasis, 

 because 27*1 per cent, were found to harbour MicrofilaricB in their 

 blood, and adult worms could be found in the lymphatics and other 

 tissues, and others (25-4 per cent.) were found to suffer from filarial 

 disease when no MicrofilaricB could be found in the blood; and, 

 lastly, in patients while still under observation the MicrofilaricB 

 have disappeared from the blood. 



etiology. — ^The causation of the various pathological phenomena 

 mentioned above is F. bancrofti Cobbold, 1877 (p. 633), introduced 

 into the body by the bite of a mosquito. 



The known carriers of the worm, as given by Theobald, are Culex 

 fatigans W^iedemann, 1828; Mansonia uniformis Theobald, igoi; 

 M. pseudotitillans Theobald; Pyretophorus costalis Loew, 1866; 

 Myzomia rossii Giles, 1899; Myzorhynchtis nigerrimtis Giles; M. 

 minulus Theobald, 1903; Cellia alhimana Wiedemann, 1821; Stego- 

 myia pseudo-scutellaris Theobald, 1910; while the worm is known to 

 be capable of undergoing a part of its development in certain other 

 mosquitoes already mentioned in Chapter XXIV. 



The reason of the non-completion of full development in any and 

 every mosquito is not known. 



After development in the thoracic muscles of the mosquito the 



