FILARIA TRANSMITTERS 315 



Finally, the last step in the process of filarial infection remained obscure 

 until 1908, -R-hen it was made known by Fiillebom. This is the mode of entry of 

 the worms into the body of the vertebrate host. It was supposed that the filari^e 

 gained access to the body directly through the wound inflicted by the mosquito 

 and while it is engaged in sucking. This Fiilleborn disproved, both by careful 

 direct observation and by long series of preparations of skin with the parasites 

 in the act of penetrating. 



" According to the suppositions of most authors the place at which the filariae 

 enter the skin is through the channel made by the puncture of the mosquito. 

 At this point the entrance of the filarias can not well take place during the process 

 of sucking, for between and besides the piercing setas the filariae can not pene- 

 trate because the stylets form a compact bundle which tightly plugs the channel 

 of the puncture. It is possible that they sometimes choose this prepared passage 

 after the mosquito has taken flight, for during the act of sucking, which only 

 lasts a very short time, it appears that, as a rule, they do not enter the skin at 

 all ; in my experiments I only found them in the skin when there had been an 

 interval, not too short, between the act of sucking and the cutting away of the 

 skin (involving the killing of the filariae). But that the filariae certainly do 

 not need the perforation made by the mosquito to get into the depths of the 

 skin is apparent from the fact that I also found them in the skin when no mos- 

 quito puncture had taken place and they were simply placed upon the skin of 

 the experimental animals ; they evidently behave similarly to the Ankylostoma 

 larvae, a supposition which Eysell has also expressed." 



MOSQUITOES THAT TRANSMIT FILARIASIS. 



The full development of the filarial larvae, and consequently their transmis- 

 sion, can only take place with certain species of mosquitoes. In others the 

 embryos are either digested or eliminated through the digestive tract, or they 

 undergo a partial metamorphosis and then die. 



In the case of Filaria bancrofti a number of species of mosquitoes are effective 

 hosts, but in an unequal degree. The most important transmitter of this para- 

 site is evidently Culex quinquefasciatus, the common house-mosquito of the 

 tropics. This is the species which has been used by Bancroft in Australia under 

 the name Culex ciliaris, by Manson in China and by Low in Santa Lucia under 

 the name Culex fatigans, and by Lebredo at Havana as Culex pipiens. There is 

 every reason for believing that these observers all had this same mosquito, which 

 is so widely distributed and abundant throughout the tropical and subtropical 

 regions. James, in India, found Anopheles rossii, and a second undetermined 

 species of the same genus, to be efiScient hosts ; the same was found to be true 

 with Anopheles costalis by Annett, Button and Elliott in West Africa. For 

 Italy and Spain Anopheles maculipennis, A. hifurcatus, A. pseudopictus and 

 Culex penicillaris are reported as transmitters. The identification of this last 

 mosquito seems open to doubt. Other species of mosquitoes in which Filaria has 

 been found to develop are Anopheles annulipes, A. alhimanus, A. minuius, A. 

 nigerrimus, Aedes calopus, Mansonioides uniformis and Mansonia pseudo- 

 titillans ( ? = tHillans) . James, in his experiments, found that Filaria bancrofti 

 developed partially in Culex microannulatus and Aedes scutellaris. 



