Parasites. 291 



large numbers, these parasites occur in a single drop of 

 blood. In the mosquito's stomach a few of the parasites 

 may undergo a developmental metamorphosis resulting 

 in the formation of embryonic forms. These latter when 

 the mosquitoes go to the water to deposit their ova, with- 

 out doubt also obtain access to the water. What more 

 probable than that they are in this condition imbibed by 

 man with his drinking water, and so are enabled to 

 undergo further development in the stomach of human 

 beings. Here again there is another example of para- 

 sitic disease, the parasite on which it depends having in 

 one stage of its existence to pass through an interme- 

 diary host — in this instance the mosquito — before it can 

 attain to the full developmental stage at which it 

 becomes injurious to man. And the moral of this highly 

 interesting piece of experimental investigation results in 

 nothing more or less than the absolute necessity of 3 

 pure water-supply. As Manson says — "the impossi- 

 bility of permanent and thorough cure of elephantiasis 



is apparent The prospeft on 



the side of prevention is much more hopeful ; for, if 

 people in countries where the filaria is endemic would 

 but cover their wells or water-jars with a netting suffi- 

 ciently fine to keep out the mosquitoes, or if they filtered 

 or boiled their drinking water, they would never get the 

 filaria or the disease it produces, elephantiasis." 



That its connexion with the mosquito is more than 

 likely gains weight by the peculiar faft, which anyone 

 can verify for himself that it is only towards night- 

 time that the filaria can be found in the blood of human 

 beings, commencing about 6 p.m. and gradually in- 

 creasing in number till midnight, after which a gradual 



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