Prevention and Eradication 57 



The former is the line of attack suited to the conditions under 

 which bilharziosis is acquired in large towns ; the latter is 

 applicable to country villages and districts. 



Peevention of Bilharziosis in Towns. 



It has been shown earlier in the report that bilharziosis is 

 frequently contracted by young children in the city of Cairo. The 

 infection could have been derived only from the public water 

 supply, and it was suggested that the unfiltered water supplied 

 throughout Cairo by pipes for garden and stable purposes was the 

 most likely source. This water is pumped from the Nile where 

 infections are known to have been contracted. It has been our 

 experience that very few gastropod molluscs could be found 

 on the banks of the Nile in the neighbourhood of Cairo. It is 

 obvious, therefore, that preventive measures applicable to Cairo 

 and similarly situated large towns should be directed to the 

 destruction of the cercaria in the water taken from the Nile. The 

 ideal, of course, would be to do away with the unfiltered supply 

 entirely. It is said, however, that such a course would deprive 

 Cairo of its gardens and would meet with tremendous opposition. 

 As this unfiltered water must be a continual source of grave risk 

 to the public health from other and more virulent diseases than 

 bilharziosis, it is evident that such opposition must have been both 

 strenuous and triumphant when this system of dual supply is still 

 tolerated by the authorities. Numerous experiments were made to 

 determine if infected water could be rapidly sterihzed. The results 

 of this inquiry will be detailed later in connection with the supply 

 of safe water to small bodies of men. They were entirely inapplic- 

 able to the requirements of Cairo. There is, however, one feature 

 about the bilharzia cercaria which may be used possibly to conserve 

 the unfiltered water supply ; that is the brief duration of life of the 

 free-swimming cercaria. It has been found impossible to keep the 

 cercaria alive for more than thirty-six hours. If it were practicable 

 to store Cairo's daily requirement of unfiltered water for two days or 

 a day and a half, there is no doubt that it would become practically 

 free from danger as far as bilharziosis is concerned. It may be 

 noted, however, that it would at the same time lose that heavy 

 sediment which has a distinct manurial value. Against this loss 

 may be set the fact that, under the present system, one-third of the 

 thirty thousand children born annually in Cairo become infected 

 with bilharzia. 



