GENERAL REMARKS 229 



(3) The disposal of excreta. 



Failure in this measure causes apparent epidemics of ankylo- 

 stomiasis. 



(4) Religion. 



Taenia solium is carried in pork and is practically unknown in 

 Mohammedan countries. 



(5) Temperature. 



If the temperature is not sufficiently high, ankylostomes cannot 

 develop. Meteorological conditions must be favourable for the 

 growth and development of the parasite and its host. 



(6) The control of the water supply. 



The Guinea-worm is commom where the water in the village 

 pond is used for washing purposes at one side and drinking 

 purposes at the other. In China, men defjecate into ponds, the 

 fishes consume the excreta, while at the other side are men fish- 

 ing and devouring the results of their sport, becoming infected 

 consequentlv with Clonorchis. 



(7) Carriers. 



Soldiers from the Boer War came home with bilharzial haemal- 



uria and infected others in England in this way. 



Some pigmies from Central Africa came to London bringing 



with them Necator americanus. 

 ((S) Domesticated animals. 



Where sheep-rearing is common, the Echinococcus prevails as 



in Australia. 

 (9) The distribution of the intermediate host. 



Snails and slugs are necessary for Flukes. 



The Bothriocephalus cannot spread without special species of 



fish. 



Trematodes require an intermediate host for their development. 



Theh' pathogenic action varies according to : — 



(i) The size of the worm which may cause mechanical injury as 

 the Ascaris when blocking ducts, &c., causing thereby append- 

 icitis, retention of pancreatic fluid, &c. 



(2) The position of the worm which will alter the symptoms and 

 the seriousness of the infection. A paragonimus in the lung, 

 a fluke in the liver, or a hcematobia in the bladder give a more 

 \'aried set of symptoms than a Gui'nea-A\()rm in the subcutaneous 

 tissue of the leg. 



(3) The number present, as when several lunibricoides form a coil 

 and cause intestinal obstruction. 



(4) The condition of the host. Ascarides mav be harmless in a 



