E. HISTOLYTICA CYSTS! DESICCATION 



by a host may also continue their development ; if so, then 

 all cysts may be infective regardless of the number of 

 nuclei they contain. 



Viability of cysts outside of the body. Desiccation, 

 From the public health viewpoint it is important to know 

 how long cysts remain viable outside of the body under 

 various conditions. In the first place moisture is necessary 

 for long-continued existence, since cysts, although pro- 

 vided with a resistant wall, are really very delicate and 

 soon perish if dried. Thus Kuenen and Swellengrebel 

 (191 3) found that desiccation killed the cysts instantly, 

 a result confirmed by Wenyon and O'Connor (1917) 

 both for cysts allowed to dry in fecal material in the 

 laboratory and for cysts contained in the dried droppings 

 of flies that had fed on infected stools. The distribution 

 of viable cysts in a dried condition in dust is therefore 

 impossible. 



The dispersion of cysts in nature. Most cysts in nature 

 remain in the raw feces in latrines until they die or 

 are carried away by flies and other animals, or on the 

 surface of the soil where they are destroyed by desicca- 

 tion, are carried away by animals, or are washed into 

 the soil or into ponds and streams by the rain. Boeck 

 (1924a) recovered E. histolytica cysts from 10 of 201 

 privies examined in one of our Southern cities. The via- 

 bility of cysts in raw and diluted feces thus becomes an 

 important public health subject. Another very important 

 point is the possibility and probability of their dissemina- 

 tion by flies and other animals. 



Tests of the inability of cysts. Some method of deter- 

 mining whether or not cysts are alive is the first requisite 



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