76 Beport of flip Billiarzia Mission in Egi/jit, 1915 



As we have seen (p. 52) the extension of perennial irrigation 

 in the past has been accompanied by a similar extension of bilharzia 

 infection. The bilharzia-carrying fresh-water molluscs cannot 

 live in saltish water. Every effort should be made, therefore, in 

 the future reclamation of the salted lands in the north of the Delta 

 to ensure, as far as possible, that favourable conditions are not 

 created at the same time for their colonization by the bilharzia- 

 spreading molluscs. 



Fig. 37.— The relations of villages to the canals. A, village on either bank of a 

 main or secondary canal; B, village on a tertiary canal; C, village between two 

 tertiary canals. 



(1) If the banks of main canals or drains are used as roads 

 the water should be adequately protected from contamination. If 

 possible, however, the roads should run between the terminations 

 of two systems of tertiary drains. 



(2) Villages should not be made on the main drains or on the 

 primary or secondary canals. They should be located as far as 



