MAN AND THE WEB OF LIFE 91 



indoors of the blood-sucking "stable-fly" (Stomoxys calcitrant), 

 in regard to which there is a strong suspicion that it may have 

 something to do with carrying the infection of infantile 

 paralysis. 



Even flies which are not blood-suckers are important as 

 distributors of disease-germs. That the common house-fly 

 (Musca domestica) helps to spread the microbes of typhoid 

 fever seems certain ; and in regard to summer diarrhoea of 

 infants, dysentery and cholera, the evidence is " very con- 

 vincing, both circumstantially and experimentally, but still 

 requires a critical attitude." l 



For diffusing Egyptian ophthalmia and other eye-diseases 

 the common house-fly and the lesser house-fly (Fannia 

 canicularis) are probably in part responsible. 



It is certain that the house-fly is a serious drag on the 

 wheels of the chariot of civilisation, and that it is incumbent 

 on man to find cleaner and thriftier ways of disposing of the 

 manure and other refuse in which flies breed. " A crusade 

 against flies must aim at prevention rather than destruction, 

 and must be applied against the insects in the early stages of 

 their existence. The injunction, ' Kill that fly,' implies a 

 confession of failure in sanitation " (Buchanan). 



We must not say more regarding insects as carriers of 

 disease-organisms ; every one knows that lice spread typhus, 

 and there are sundry ticks .which are deadly disseminators, 

 as of " tick-fever " in man and " red- water " in cattle. 



One of the great life- savers during these tragically 

 destructive years has been Dr. Leiper, who discovered in 

 Egypt the life-history of the formidable worm (Schistosoma 

 haematobium) which causes the serious disease of bilharziasis 

 in man. In some parts of Egypt this disease affects every 

 third person, and as the tiny, free-swimming, juvenile stage of 

 the worm usually enters through minute cracks in the skin, it 

 is very difficult for people who have contact with unfiltered 

 water to evade it. Dr. Leiper showed that part of the early 

 life is passed in several fresh-water snails, so that a check to 

 these will check the malady ; and, moreover, that the free- 



1 See R. M. Buchanan, Insects in Relation to Disease (Glasgow, 1916). 



