636 



NEMA THELMINTHES 



These MicrofilaricB occur in the peripheral blood at night, as 

 has just been stated, beginning about 5 to 7 p.m., and increasing 

 in numbers till midnight, and then diminishing till about 7 to 8 a.m., 

 when only a stray one may be met with, as, indeed, can be observed 

 all through the day until the evening increase begins. There is, 

 therefore, a definite periodicity- — at night the MicrofilaricB abound 

 in the blood, while in the day-time they do not. 



In the day it appears that they live mostly in the lungs and in 

 the large vessels of the thorax. This was shown by Manson by the 

 careful examination of films and sections taken from the different 

 organs of a man who had Microfilaria bancrofti in his peripheral 

 blood, as well as a Ijnnph scrotum and varicose groin glands. 

 The post-mortem was made six hours after death, which took place 

 almost instantaneously at 8.30 a.m., being due to drinking hydro- 

 cyanic acid. By far the largest number of parasites were to be 

 found in the lungs and carotid artery, and then in the heart muscle, 

 while a few were found elsewhere, especially in the kidney. 



Fig. 269. — Microfilaria bancrofti Cobbold. 



These facts have been confirmed, but the question as to what 

 induces the parasites to live in the peripheral blood in the night 

 and the thoracic organs in the day is not clear. True, it enables 

 the Microfilaria to enter the mosquito, but that does not explain 

 the problem. Neither variations in atmospheric temperature nor in 

 pressure, in light, or in darkness seem to have any effect. Nor does 

 the pulse-rate or the individual's temperature make much differ- 

 ence; but there is one factor, first shown by Mackenzie and since 

 confirmed by Manson and others, that it is in some way connected 

 with sleep; for if a person with Microfilariae in his blood stays 

 awake all night and sleeps during the day, the parasites will 

 abound in his blood in the day, and not at night. Penel remarks 

 that the problem of the periodicity of the Microfilaria and the 

 periodicity of sleep in man are connected, and that when one is 

 properly solved the other will also be elucidated. 



Recently Bahr has shown that the microfilaria of F. bancrofti 



