LIFE HISTORY OF FILARIA BANCROFTI 299 



Africa, about 74 per cent of the men, 79 per cent of the women and 

 33 per cent of the children were found to be filariated. 



The blood-dwelling filariffi which are readily observed are, as 

 remarked above, only larvae, the adults being much larger, long, 

 slender worms which live in the lymphatic vessels, connective 

 tissue or other tissues of the body. It is to these adult worms 

 and not to the larvae that the so-called " filarial diseases " are 

 supposed to be due; the blood-living worms apparently cause 

 no serious symptoms. The larvae have been termed " micro- 

 filarise " to distinguish them from the adult worms. 



Filaria bancrofti 



The most widespread species and most important from a 

 medical point of view is Filaria bancrofti. This nematode occurs 

 more or less abundantly in all warm climates of the world, north 

 to southern United States and southern 

 Europe and Asia, and south to southern 

 Australia and Patagonia. 



Life History. — The adult Filarim 

 were not discovered for many years p^^.j.. Adults of F&ria 

 after the larvae had been found in the bancrofti, female (9) and 

 blood, since they occur in the deep- ^er MansonO^*""'' ''''' 

 seated lymphatic vessels where they could 



be observed only on post mortem examinations. They are very 

 long, slender nematodes (Fig. 122), the females three or four inches 

 in length and hardly greater in diameter than a horsehair, and 



the males about half this size. In their 

 normal habitat in the lymph vessels the 

 males and females live coiled up to- 

 gether, sometimes several pairs of them 

 Fig. 123. Microfilaria of in a knot. The male worms, in addition 

 f™"uttrff ;«Tur! to their smaller size, may be distin- 

 rounded by delicate mem- guished from the females by the coiled 

 rane. ( er a r.; ^^^j which reminds one of a vine tendril. 



The greater part of the body of the female is occupied by a pair 

 of uteri, which in the adult are always filled with eggs. 



The eggs (Fig. 123) usually hatch before they are laid so that 

 living young swarm forth from the parent worm, but in excep- 

 tional cases the eggs are deposited before hatching. The young 



c#d) ^ 



