SOME INHABITANTS OF MAN 153 



followed the careful application of hookworm larvae to the 

 skin. 



Looss' researches, the outcome of a laboratory accident in 

 the course of a purely zoological investigation, profoimdly 

 altered our conceptions regarding the mode of spread and 

 prevention of hookworm disease. Protection of water-supply 

 could only play a small and insignificant part in prophylactic 

 measures against a parasite which was likely to enter the body 

 whenever the skin came into contact with a moist contamin- 

 ated surface, for statistical studies showed that cutaneous 

 infection was actually responsible for over 90 per cent of the 

 cases investigated. 



In the parasitic infections hitherto considered it has proved 

 possible to rely for preventive measures on an attack upon 

 the special intermediary or the vehicle-host. In the case of the 

 hookworm, not only is an intermediary host absent, but the 

 terminal phase of development, i.e. the " infective " stage, 

 forms by ecdysis a pecuUarly resistant skin in which the 

 larva can survive for many months without food and with 

 a minimum amoimt of moisture. Moreover, these are spread 

 over enormous areas. 



Under these circumstances the attack has had to be trans- 

 ferred to the eggs before they are disseminated and to the 

 adulb worms. In other words, eradication of this disease 

 depends upon the efficient disposal of night-soil and upon 

 the destruction of the adult parasites living within the body. 



Fortunately the ankylostome is an intestinal worm and is 

 peculiarly susceptible to certain drugs. By treating infected 

 persons, not only are these individuals relieved of their para- 

 sites but they cease to be a source of danger to others. 



There was Uttle hope that ankylostome infection could be 

 stamped out by such measures as these so long as the cost and 

 responsibility of carrying them out depended upon the initiative 

 of infected individuals. Persons harbouring only a few worms 

 would feel no ill-effects and would therefore be unlikely to pay 

 for treatment. Nevertheless these persons would continually 

 pass living eggs in their excrement and thus be a menace to 

 others. 



