Prevention and Eradication 



61 



the head, about 42 kilometres per day, which probably falls some- 

 what lower down. On the Suez portion of the fresh-water canal at 

 40 kilometres from Ismailia, the velocity, according to Mr. Hall, is 

 0*27 metre per second — i.e., less than 24 kilometres, or 15 miles, per 

 twenty-four hoars. 



Mr. Craig, of the Statistical Department, writes, that the time 

 of flow from the Barrage to Ismailia may be taken as two days, 

 and that this rate does not vary much from low stage to high stage 



Fig. 26. —The Port Said branch of the sweet water canal at Qantara. 



of the river. From this one may conclude : {a) that any infection 

 entering the canal at its head, even during high flood, would have 

 died out before it reached Ismailia ; {b) any bilharzia infections 

 acquired in the Canal zone from the Port Said and Suez branches 

 of the canal must originate from local infection of molluscs in the 

 Ismailia Canal. In the stretch from Cairo to Ismailia the canal is 

 very free from vegetation, and molluscs are relatively very rare. 

 From Ismailia to Qantara, and from Ismailia to Suez, the amount 

 of weed is so great that it is difficult to traverse these sections 



