FILAEIA SANGUINIS HOMINIS IN THE MOSQUITO. 3G9 



mosquito, when feeding on the blood of a filarious subject, imbibes the Filaria. Lewis 

 confirms me in the statement that nematodes at a stage of development slightly more 

 advanced than those found in the newly ingested blood are also to be found in the 

 mosquito. But Lewis says he could not satisfy himself that these two forms belong to 

 one and the same species of nematode. Neither he nor Sonsino has found advanced 

 forms, so advanced that from their appearance they would be justified in concluding they 

 were fit for independent life. Possibly, suggests Lewis, the more advanced forms are 

 embryos of some other species of nematode, and not the Filaria sanguinis hominis at all. 

 In my observations I paid particular attention to this point. If I succeed in connecting 

 the more advanced forms of nematode embi-yo, as seen by Lewis, with the unquestioned 

 embryo Filaria sanguinis hominis found in newly ingested blood, and with the later forms 

 which I had already described as being equipped for independent life, then there is no 

 longer any room for doubt about the role of the mosquito, and I can claim that Lewis's 

 observations confirm my own. 



I would remind the reader that the parasite called Filaria sanguinis hominis is a minute 

 nematode embryo which in certain warm countries is found in the blood of Man. It is 

 the offspring of a mature Filaria living in the lymphatic vessels. The young find their 

 way into the blood-circulation along with the lymph. 



No form intermediate between the mature Filaria and its embryo has hitherto been 

 found in Man. There is no evidence of growth about the embryo, neither has any 

 provision in its structure by which one might suppose it could pass from one man to 

 another been discovered. It seems most probable, therefore, that like many other 

 parasites it requires the services of an intermediary host — 1st, to remove it from the body 

 of the host ; 2nd, to nurse it till it becomes equipped for independent life ; 3rd, to place 

 it in a position for obtaining access to its final host. 



In our search for this intermediary host we must be sure the animal we encounter can 

 fulfil these conditions. In addition to this there are two other circumstances in connex- 

 ion with the Filaria which must also be recognized in fitting it with an intermediary 

 host. Such an animal must have a geographical distribution corresponding to that of 

 the Filaria ; and it must also be nocturnal in its habits. The reason for the first of these 

 conditions is self-evident ; the latter is indicated by the curious fact in the history of the 

 Filaria, that the embryo appears in the blood only at night. This peculiarity in the 

 habits of the Filaria has now been so frequently demonstrated and confirmed that I need 

 concern myself here only with the mention of it. 



There are many reasons why one should regard the mosquito as the animal most likely 

 to fulfil all the conditions required. These reasons I will not enlarge on. I will confine 

 myself to the description of what actually occurs in the relationship of the mosquito to 

 the Filaria, feeling satisfied that in this is the best proof that the mosquito is the true 

 intermediary host of the Filaria sanguinis hominis. 



In experimenting with the mosquito there are two points I was careful in attending 

 to ; I employed the proper species of insect, and I took care that its only food was the 

 blood of a filariated man. Those who would repeat my experiments must bear these two 

 points in mind. The plan of procedure I found most convenient was as follows : — I 



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