84 Beport of tlie Billiarzia Mission in Egypt, 1915 



would not have the requisite effect upon the activity of the bilharzia 

 cercaria. It would be necessary to use two parts of available 

 chlorine per 1,000,000, and afterwards to dechlorinate in order to 

 render water taken from the canals and ditches in Egypt free from 

 bilharzia infection. 



For troops stationed on small outposts in the Delta safe water 

 can be had, after two days, by improvising storage in tarpaulin 

 sheets, etc. Where this is impossible the drinking water should 

 be separated from ablution water and the former sterihzed by 

 boiling or by tablets of acid sulphate of soda. The ablution water 

 may he rendered quite safe for immediate use by the addition of 

 ordinary Army ''Cresol" in the dilution 1 in 10,000, 2vhile 1 in 

 90,000 is sufficient if the water is hcpt overnight. 



Practical Conclusions. 

 From the above it may be concluded that unfiltered water taken 

 from canals, ditches, or birkets would be rendered safe : — 



(1) If kept beyond the survival period of the cercaria, i.e., 

 for forty-eight hours. 



(2) If heated to 50° C, a temperature at which the cercaria is 

 immediately killed. 



(3) If previously treated with those chemicals that are lethal to 

 the cercaria. 



Attention should be given to the following points : — 



(1) Personal contact of any kind with unfiltered water is risky. 

 The surface of the water is the most likely to be infective as the 

 cercarioe congregate there. Canal water should not be "dipped" 

 for, but should be drawn by hand pump. An intake pipe should 

 always be led to the centre of the stream and should draw the 

 water from near the bottom and at a place where there is little 

 or no vegetation. 



(2) It is essential in drawing water for storage, in order to 

 destroy the bilharzia cercaria, that no infective mollusc be admitted. 

 This can be ensured by screening the intake pipe with gauze having 

 about six meshes to the linear inch. The common mosquito gauze 

 or phosphor-bronze wire gauze is very serviceable. 



(3) The water in the wells with " sakias " may be regarded as 

 much safer than that from other sources. Hitherto molluscs have 

 not been found in these wells. 



(4) Shallow barrel sand-filters afford no protection. 



(5) Although the reproductive activity of bilharzia in the 

 molluscs is most intense during the summer months there is a 

 certain liability to the infection throughout the year. 



