P. Manson-Bahr and N. H. Fairley 
(51 
Distribution of fresh-ivater snails in localities visited in Egypt. 
El Marg near 
Cairo 
Planorbis boissyi (common), Bullinus contortus, dybowski, inne-n, for shall, Physa 
subopaca (scarce), Vivipara unicolor, Bylhinia senadrica, Cleopatra bulimoides 
(very common), Melania tuberculata, Limnaea caillaudi (scarce). 
Zag-a-zig to f Bullinus contortus and dybowski, Planorbis boissyi, Limnaea caillaudi, Cleopatra 
Ismailia ( bulimoides, Physa subopaca, Melania tuberculata, Planorbis mareoticus. 
KantaraTanks Bullinus dybowski, Physa subopaca. 
Southern Canal f Bullinus dybowski (much the commonest species), Bullinus contortus (rarer). Very 
Zone \ few Planorbis boissyi. Amongst 1000 Bullinus there were only three Planorbis. 
Cairo 
(\. Head Storage Reservoirs. Abbassia (unfiltered water supply) water collected 
directly from the Nile. 
Bullinus contortus (very common). 
Bullinus dybowski. 
Limnaea caillaudi. 
Melania tuberculata. 
Planorbis boissyi. 
2. Snails from unfiltered water-pipes. 
-< Cleopatra bulimoides. 
1 Melania tuberculata. 
i 3. Public Ponds. 
Limnaea caillaudi. 
4. Snails from receding Nile at Agu Baba in mud. 
Vivipara unicolor. 
Cleopatra bulimoides. 
Bythinia senaarica. 
k Melania tuberculata. 
VI. THE INCIDENCE AND ORIGIN OF BILHARZIAL INFECTION 
AMONGST THE CAIRENES. 
As Australia is faced with the potential danger of outbreaks of bilharziasis, 
the following observations on the manner in which the natives of Cairo are 
infested may be of importance. 
Looss, in an investigation of the percentage of infested children in Cairo, 
found.33 per cent, of the boys at a certain school to be infested with S. haema¬ 
tobium. In 1908, Mrs Elgood showed that 27*5 per cent, of the girls attending 
a school in Cairo were similarly infested. 
The supporters of the “Looss hypothesis” maintained, that as the children 
had never been out of Cairo, and as there was a common filtered water supply 
to the white and native population of Cairo alike, direct miracidial infestation 
was the only explanation that would account for the distribution of bilharzi¬ 
asis amongst them. 
In criticizing the supporters of the “Looss theory,” Leiper pointed out the 
presence of a second water system carrying unfiltered water from the Nile, 
and used ordinarily for supplying public and private gardens. This water, 
