274 DISEASES DUE TO HELMINTHS 



The embryo is set free and is discharged from the genital pore. It is 

 then free in the lymph stream in which the adult female happens to be. 



The Embryo. — The embryo or Microfilaria nocturna passes from 

 the lymph stream to the thoracic duct, the right heart and lungs to the 

 peripheral circulation where it is to be found at night. 



These Microfilaria wriggle about in the blood-stream, moving the 

 blood cells to and fro, but without making progress. They are about 

 300 bv 8 fj,, with rounded anterior and tapering posterior ends. 

 They are enclosed in a sheath, longer than itself, inside of which it 

 darts to and fro. Were it not for these sheaths the embryo might use 

 its anterior spine to escape through the wall of the blood-vessel, and 

 so avoid the mosquito that transmits it. 



A thick proboscis carries the spine, which can be covered by a 

 retractile and protractile six-lobed prepuce. 



The dermo-muscular transversely striated body encloses many 

 granules whicli are wanting in definite parts of the parasite thus — 



(i) In the anterior extremity of the body (not the sheath). 



(2) In a transverse spot, 21 "5 per cent, of the whole length from the 

 anterior extremity. 



(3) In a \'^-shaped spot, 30 per cent, of the ^hole length from the 

 anterior extremity. 



(4) In a median line, the centre, 63 per cent, of the whole lenglh 

 from ithe anteritM" extremity. 



(5) In an oval spot (tail spot), 85 per cent, of the whole length 

 from the anterior extremity. 



(6) In a central spot, 91 '5 per cent, of the whole length from the 

 anterior extremity. 



The significance of these granules is not known. 



Its Habits in Man. — They are to be found in the peripheral blood 

 ar night from 5 j).m., increasing to midnight, then until 8 a.m. 

 diminishing. During the day they live in the lungs, large thoracic 

 vessels, carotid artery, heart, muscle and kidney. 



If man sleeps during the day instead of at night the periodicity 

 will be reversed, but not completely, hence sleep may have something 

 to do with its periodicity. 



The common carrier, Culex fatigans, biles at night, but the carrier 

 in Fiji, Stegomyia pseudo-scutellaris, bites in the daytime, and Bahr 

 says that there the Microfilaria are found in the blood during the day- 

 time also, so that the periodicity is controlled bv the habits of the 

 more efficient insect host. How the Microfilaria maintain their 

 position against the blood-stream has not been shown. One blood 

 film may show as many as 500 embryos. It has been calculated that 

 there may be 45,000,000 in a fully grown man. 



