MOSQUITOES AND FILARIASIS 



141 



They are found in abundance in the blood duiin<j; the 

 night or during sleep, but during the day, or, rather, 

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

 seems to be no good exj)lanation 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 Head and Beak of ]\Ios(juifo, showing Filarias 

 entering Beak; enlarged. (Redrawn from Britis/i Medical Jounml.) 



mosquito, which serves as an intermediary host. Having 

 more than twenty 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 the transmission of the disease, and his 

 subsequent observations proved the correctness of this 

 idea. The Filaria embryos, according to his observa- 



