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CHAPTER XVII. 

 PROPHYLAXIS IN PROTOZOAL DISEASES : RESUME. 



(I) General Prophylaxis. Few of the protozoa are 

 known to be carried under natural conditions directly 

 from man to man. As a rule an intermediate develop- 

 ment of the parasite has to take place before it can again 

 re-enter man. In many cases this development only 

 takes place in a suitable alternative host mosquito, 

 biting fly, bug, or tick ; in others, the further develop- 

 ment can take place on the ground or in water. 



Where an alternate host is required prophylactic 

 measures must be directed not only against the patho- 

 genic parasite but also against the intermediate host, so 

 that detailed knowledge of the life-history of these hosts 

 is required. 



As a general rule, where the parasites are found in the 

 blood or where the blood is infective a blood-sucking 

 intermediate host is required. Where the parasite exists 

 in the intestinal canal or in the skin no such host is 

 necessary. For each disease, therefore, there will be 

 differences in detail as to the prophylactic measures 

 required. 



(II) Special Prophylaxis. With the intestinal diseases 

 prophylaxis depends (i) on the success of the methods 

 adopted for the disposal and destruction of excreta, and 

 (2) preservation of the water supply from all possible 

 sources of contamination and the uniform use of thorough 

 boiling or efficient filtration to destroy any of these 

 infective forms in water and milk. 



