54 Beport of the Bilharzia Mission in Egypt, 1915 



basin irrigation. This has been remarked upon by Milton. In the 

 Kecords of the Egyptian Government School of Medicine for 1904 

 he states : — 



" Cairo is on the dividing line between Upper Egypt and the 

 Delta, and patients come to Kasr-el-Ainy for treatment from all 

 parts of the country ; still the disproportion betvi^een the number 

 of cases of bilharzia drawn from the two natural divisions of the 

 country is so very marked that there must be some very well 

 defined cause constantly acting, and this, I believe, is to be found 

 in the way in which water is supplied to the different provinces for 

 the purposes of irrigation. The provinces of Lower Egypt are 

 supplied with water for irrigation all the year round, or practically 

 so, whereas the Upper Provinces are supplied with water for 

 irrigation only during and after the time of High Nile. Thus the 

 peasant from Lower Egypt has a much longer period of time during 

 which he is exposed to the chance of infection, and infection is 

 more frequently repeated than is the case with his brother of the 

 Upper Provinces. 



" The province of Ghizeh is a case very much in point, for here, 

 although it borders immediately on Cairo, and although Cairo is its 

 hospital town, the proportion of its population per 100,000 coming 

 for treatment for bilharzia is but 9'75 as compared to Sharkieh 

 19-85, Qalioubieh 18-06, and Menoufieh 13-47, the three other 

 provinces adjoining the capital, but then Ghizeh is basin irrigated, 

 whereas the other provinces named are perennially irrigated." 



The relative frequency of bilharziosis in pert 'ally irrigated 

 areas may be due in part to continued liability of i e workers to 

 infection as suggested by Milton, but the favourabu environment 

 created for the propagation of the intermediate host i^ ^bably a 

 much more important factor. 



Subsoil water is generally derived from local 



"^ JJ^^ ■ rainfall, but in Lower Egypt it is pr^.-^tically all 

 ' the result of seepage from the Nile and its canals. 

 The average thickness of the Nile alluvium is said to be about 

 seven metres, below this is a layer of sand and gravel into which 

 the river-bed dips. Through this layer, when the river is in flood, 

 a natural flow of water takes place and the static head of the 

 river in flood is thus transmitted to great distances, causing a 

 rise in the level of the subsoil water. This rise is sometimes 

 actually visible, for low-lying land near the river may become 

 covered with water. The subsoil water of the deep sand and gravel 

 strata is utilized for the water supply of towns and for purposes 



