Other Diseases Transmitted by Insects 165 



When these parasites are withdrawn from the circu- 

 lation and placed on a slide for study they are seen 

 to be minute transparent, colorless, snake-like or- 

 ganisms inclosed in a very delicate sack or sheath. 

 They are but a little more than one-hundredth of 

 an inch long and about as big around as a red 

 blood-corpuscle. These are the larval forms of the 

 parasite and have been called by Le Dantec the 

 micro-filaria. 



If blood of the patient drawn from the skin, is 

 examined during the day few if any of these para- 

 sites are found, but if it is examined between five 

 or six o'clock in the evening and eight or nine 

 o'clock the next morning they may be found in 

 numbers. During the daytime they have retired 

 from the peripheral circulation to the larger arter- 

 ies and to the lungs, where they may be found in 

 great numbers. 



This night-swarming to the peripheral circu- 

 lation has been found to be a remarkable adapta- 

 tion in the life-history of the parasite, for it has been 

 demonstrated that in order to go on with its de- 

 velopment these larval forms must be taken into 

 the alimentary canal of the mosquito. Most of the 

 mosquitoes in which the development takes place 

 are night-feeders, so that the parasites are sucked 

 up with the blood of the victim. Once inside the 



