Adiilfs and Ova 123 



It may be that the large cercaria occasionally seen in P. holssiji at 

 Marg is the infective stage, but of this there is no evidence save that no 

 other Egyptian mammal is known to harbour Bilharzia. 



At first it had occurred to me that these differences in size might be 

 accounted for by the separation of the sexes in the bilharzia worms in 

 contrast to the normal state of hermaphroditism prevailing among the 

 Trematodes. 



In his postulates Looss had argued in favour of sporocysts giving rise 

 to adults of one sex only, to explain the frequent presence of males only in 

 an infected person. This highly suggestive hypothesis may well prove 

 true for the sporocysts and their resulting cercaria? in the molluscan host. 



Experience shows that if the cercariae discharged from one specimen 

 only be used for experiment, the resulting worms may be of one sex only. 

 Owing to the extreme fragility it was impossible to isolate a single "tube" 

 of cercarife from an infected liver and so put the matter to experimental 

 proof. Experimentally infected animals, like naturally infected persons, 

 usually show a marked predominance of male over female worms. This 

 would seem to be a happy provision of nature to ensure that no female that 

 had successfully gained her way into the final host should lack opportunity 

 of producing offspring. 



There is one other matter relating to the bilharzia 

 Other problem as presented by the village Marg which was for a 

 ROBLEMs. j^^^g ^j^^^ puzzling, but for which a tentative explanation 

 may be suggested. Urinary bilharziosis prevailed among the children in 

 Marg to the extent of ninety per cent. The incidence of intestinal and 

 particularly Manson's intestinal bilharziosis could not conveniently be 

 ascertained. The presence there of infection with lateral-spined eggs was 

 revealed by the find of specimens in the urine of one of the infected 

 children. Now in the small canal within the confines of the village, 

 P. hoissiji w^as relatively more frequently infected wnth cercariae, i.e., with 

 P. mansoni than was Bullinus with B. hannatohia. After many visits 

 the habits of the residents became fairly well known. The shelving banks 

 of the canal served as a public latrine. The sides and uncovered bed of the 

 channel were strewn with faecal deposits. The Egyptian squatting for the 

 purpose of defaecation faces the bank to observe anyone approaching. 

 Consequently, any urine discharged falls on to the dry surface at a higher 

 level than that at which the stool is deposited. This urine sinks into the 

 dry soil leaving bilharzia eggs on or near the surface where they are 

 exposed to the destructive effect of sun and wind. The eggs passed in the 

 fseces are not so readily killed. It is well known that bilharzia eggs will 

 remain alive and unhatched, in a fairly consistent stool, for weeks under 

 suitable conditions. At Marg the level of the water in the canal rises and 

 falls with a varying periodicity owing to the control in the amount of flow 

 by the irrigation department. The consequence is that the sides of the 

 canal, and especially the flatter portions of the bed, are automatically and 



