MOSQUITOES AND FIL ARIA SIS 



141 



They are fonud iu abuudaiice iu the blood durini;' tbe 

 uiglit or during sleep, but duriug the day, or, rather, 

 while the patient is awake, they cannot be found. There 

 seems to be no good explanation of this periodicity, nor 

 is it absolutely exact, but it constitutes a very curious 

 adaptation of the parasite to the nocturnal habits of the 



Fig. 36. —Cross Section of Hend and Beak of IMosquito, sliowing- Filarias 

 entering Beak; enlarged. (liedrawn from British Medical Jon nia/.) 



mosquito, which serves as an intermediary host. Having 

 more than tAventy years ago proved this periodicity of 

 the embryos, Dr. Patrick Manson had the happy thought 

 that as mosquitoes bite men during sleep, perhaps they 

 may be agents in th(3 transmission of the disease, and his 

 subsequent observations proved the correctness of this 

 idea. The Filaria embryos, according to his observa- 



