162 TROPICAL MEDICINE AND HYGIENE 



invaded by them. The eggs of ankylostomes and young 

 larvae are destroyed in the course of their passage through 

 the intestines of these dipterous larvae. For this to take 

 place the muscid larvae must be of species that will live 

 in the contents of a cesspit till ready to pupate. 

 Young muscid larvae do not feed sufficiently voraciously, 

 and the larvae of flies like Musca domestica that soon 

 leave the faeces are of little value. In other cases, where 

 the cesspits are merely holes in the earth, and there are 

 no or few dipterous larvae, the ankylostome larvae pass 

 into the earth, so that the soil of the neighbourhood of 

 the cesspits becomes infective. This is preferable to the 

 widespread infection that takes place where defaecation 

 is diffuse. In brick, cement, or other impervious cesspits, 

 the decomposing faeces do not form a suitable medium 

 for the development of the larvae and they soon die. In 

 a septic tank they are rapidly killed. In the manufacture 

 of poudrette the eggs and larvae of ankylostomes are 

 completely destroyed, both when the powder is made by 

 air drying on an impermeable floor or by the application 

 of artificial heat. 



The prevention of the spread of ankylostomiasis can 

 therefore be effected by many methods of disposal of 

 sewage. The dangerous methods are deposition on the 

 surface of the ground, superficial burial, and even shallow 

 trenching whilst the faeces are fresh. 



In mines a good deal depends on the degree of acidity 

 of the water in the mines. In the Transvaal, according 

 to Turner, though the acidity varies, according to depth, 

 age, &c., there is usually a considerable degree of acidity 

 due to sulphuric acid from decomposing pyrites. An 

 acidity of over o- 1 per cent, sulphuric acid will prevent the 

 formation of larvae, and this is exceeded in some of the 

 mines. Boycott has also shown that 2*5 per cent, of salt 

 solution rapidly destroys larvae. 



Triodontophorus. Small sclerotomes first found in 

 equines in Egypt and subsequently in the gorilla. In 

 man a species, Triodontophorus deminutus, was found in 





