i8o 



CHAPTER XV. 

 PROPHYLAXIS. RESUME. 



General Prophylaxis. The life-history of each parasite 

 has to be considered for economical and effective pro- 

 phylaxis. There are many important gaps in our know- 

 ledge, particularly of the parasites with a complicated 

 external life where intermediate hosts in all probability 

 are essential. All Schistosomidae are instances of this, 

 and even as regards the Fasciolidae and Paramphistomiclae 

 parasitic in man a knowledge of the habits and species 

 of the hosts would be an important aid in the prevention 

 of infection. In considering the prevention of infection 

 with parasites whose life-history in whole or part is 

 known, we have to take into account : 



(1) How the parasite, eggs, embryos, or larvae leave 

 their host (man or other animals). 



(2) What happens to them afterwards. 



(3) How they re-enter their host (man). 



(i) All parasites inhabiting the alimentary canal, the 

 bile-ducts, and in some cases the vessels in the vicinity, 

 leave man as eggs or larvae in the faeces. These include 

 TREMATODES, e.g., Fasciolopsis buski and F. rathouisi, 

 Opisthorchis noverca, Clonorchis sinensis, Heterophyes hetero- 

 phyeSj Gastrodiscus hominis, Watsonus watsoni, Schisto- 

 somum japonicum, S. hcematobium (sometimes), and 

 S. mansoni, as well as the Trematodes that are accidental 

 parasites of man. All Cestodes except the Echinococcus. 

 NEMATODES : Ascaris Inmbricoides, Trichocephalus dispar, 

 Ankylostonium duodenale, Necator americanus, Oxynris 

 vermiculariSj Strongyloides intestinalis ; as well as rarer 

 Nematode parasites : Strongylus subtilis, Triodontophorus 

 deminutus, Physaloptera mordens, &c. 



