286 



THE ANIMAL PARASITES OF MAN 



up with the bloo'd by mosquitoes in the process of sucking ; how- 

 ever, whilst for the malaria parasites of man only the genus 



Anopheles comes into consideration, the larvae 

 of Filaria immitis thrive equally well in 

 Anopheles and Culex. The conditions, how- 

 ever, are not quite alike, because Cule% 

 pipiens is not so easily infected. The 

 filarial larvae, however, leave the stomach 

 of the mosquito, and penetrate into the 

 malpighian tubes or their epithelial cells. 

 They here undergo a series of changes, 

 moult, and on the twelfth day after the 

 infection of the mosquitoes perforate the 

 organ they have been inhabiting, and thus 

 reach the body cavity, which communicates 

 with the labium ; by penetrating into the 

 thorax, the larvae, which have attained a 

 length of O'9 mm., reach the head and 

 finally the labium, where they await until 

 the mosquito bites a dog. Though the, 

 labium is not introduced into the wound 

 made in biting, but bends backwards, forming 

 an angle, yet during the process it tears its 

 very delicate cuticle, and the larvae avail 

 themselves of this rent to escape. They 

 penetrate between the labium and the sty- 

 lets, thus finding the wound, which enables 

 them to enter into the vascular system. In 

 order to meet the objection that the dogs 

 infect themselves per os that is to say, by 

 biting and swallowing infected mosquitoes 

 swarming around them, the experimental 

 animals were prevented (by muzzles) from 

 devouring the mosquitoes. These experi- 

 ments also succeeded. 



[Grassi and Noe's theory as to the mode 

 of escape of Filaria immitis is untenable. 

 The filariae escaping through a rent of the 

 labium at the part which bends during suc- 

 tion would be unable to reach and penetrate 

 the wound made by the lancets. In a paper 

 published in the Journal of Tropical Medicine^ Dr. Button suggested 



. \ 



FIG. 195. Filaria 

 immitis, natural size ; the 

 male is on the left and 

 the female on the right 

 side. (After Railliet.) 



'August I5th, 1901. 



