382 DR. P. MANSON ON THE METAMORPHOSIS OF 



blood in the evening with the same results as in coolie No. 2 ; it contained plenty of 

 Filarice. 



Coolie No. 4 brought six mosquitoes with this result, that three of them when ex- 

 amined ninety-six hours after capture were found to contain Filar ice, and three of them 

 yielded no parasitic form whatever. This man's blood was examined at 9 p.m., and, like 

 that of coolies No. 2 and 3, was found to contain many Filarice. These coolies all came 

 from Hoorcoah, a district to the north of Amoy, in which a very large proportion of the 

 inhabitants are filariated. 



It was now evident I must examine mosquitoes from some less questionable feeding- 

 ground before I ventured to draw any conclusion from this endeavour to prove a negative. 

 I had a boy of about 15 years of age for a servant ; he was healthy and his blood did not 

 contain Filarice. I got this lad to bring me his mosquitoes, with this result : — Eight 

 mosquitoes examined sixty-four hours after capture — no Filarice found ; one mosquito 

 examined eighty hours after capture — no Filarice ; one mosquito examined eighty-eight 

 hours after capture — no Filarice ; five mosquitoes examined one hundred and four hours 

 after capture — no Filarice. I examined a few mosquitoes fed on other non-filarious 

 individuals, and with the same negative results. 



Many years ago, in searching for the intermediary host of the Filaria immitis, I ex- 

 amined many tens, if not hundreds, of mosquitoes that had fed on dogs' blood ; but in no 

 instance did I remark, although I was on the outlook for such, an advanced form of 

 filarial development. 



Lewis also did not find sausage-shaped nematodes in any mosquitoes but in those that 

 came from a certain room where it was afterwards discovered that a filariated man slept. 

 He examined with a negative result many mosquitoes that had preyed on the blood of 

 dogs or birds. 



Similarly Sonsino found Filaria? in about half his mosquitoes ; they were captured in 

 a bed where two men slept, one of whom had Filarice in his blood, whereas the other was 

 not thus infested. 



The inference from these facts is obvious. It is only mosquitoes that have fed on the 

 blood of filariated men that contain the developmental forms I have described. 



In the foregoing I think I have conclusively shown that the mosquito fed on filariated 

 human blood ingests the embryo Filaria sanguinis hominis, that while in the mosquito 

 the Filaria undergoes great developmental changes, and that it finally quits this insect as I 

 a large and powerful animal equipped for an independent life. I have also shown that the 

 mosquito fed on non-filaviated blood exhibits, when dissected, no such parasitic forms. I 

 therefore infer that the parasitic forms I meet with in the mosquito fed on filariated blood 

 are really advanced forms of the embryo Filaria ingested with the blood, and that the 

 mosquito is the proper intermediary host of the Filaria. I do not see how this inference 

 can be avoided. It would be much more satisfactory, and an easier method of demon- 

 stration, could we watch an individual Filaria in its progress from the circulation down 

 the proboscis of the mosquito into its stomach, watch it wriggling there, case its skin, 

 and, changing its method of movement, worm its way through the tissues into the 

 thorax, become passive there among the muscles while it acquired size, an alimentary 



