xiii, b, 2 Haughwout: Infections with Coccidium 85 



adds that the possibility of infection through association with 

 animals that are passing the oocysts in their faeces must be 

 investigated. 



The belief is current that the cysts of coccidia are exceedingly 

 resistant to untoward environmental conditions. Apparently 

 they are much more resistant than the cysts of species of En- 

 tamoeba. It must, however, be said that their impermeability 

 makes it exceedingly difficult to determine whether they are 

 living or not, by the application of the eosin test, which gives 

 such excellent results in the case of Entamoeba. The depart- 

 ment of medical zoology is at present conducting a series of 

 tests to determine how long they will retain their vitality under 

 approximately normal and under experimental conditions. This 

 is an investigation that will consume considerable time — several 

 years in fact, but our preliminary investigations show us that 

 they are extraordinarily resistant to a variety of reagents that 

 quickly kill the cysts of Entamoeba. I have watched, under the 

 microscope, the development of cysts of Isospora bigemina in a 3 

 per cent solution of potassium bichromate, in water treated with 

 thymol, and in double-strength Gram's iodine solution, and I 

 have even seen cysts that would resist the application of Bouin's 

 picro-aceto-formol solution for more than four hours. Other 

 workers have reported on the resistance of coccidial cysts to 

 desiccation, but it is too early to report anything on this from 

 our laboratory. 



It would not be surprising to discover that these cysts remain 

 viable after two or even three or more years. Indeed the 

 cysts of Coccidium avium have been shown to be infective two 

 years after passage from the intestine of the infected fowl. (7) 

 Mast (14) has shown that the cysts of Didinium nasutum, a free- 

 living infusorian, will retain their vitality for a period of five 

 years in air-tight vials. He has found that drying in ordinary 

 atmospheric conditions does not destroy the cysts. In fact, he 

 believes they will live longer dry than in a solution. 



However, Wenyon and O'Connor (24) corroborate Kuenen 

 and Swellengrebel in their assertion that the cysts of Entamoeba 

 histolytica will not withstand drying. They add that cysts of 

 this parasite will survive for thirty days in water, again con- 

 firming Kuenen and Swellengrebel. They point out the im- 

 portance, however, of making a considerable dilution with water 

 to keep down bacterial and fungoid overgrowths that tend to 

 destroy the cysts. 



This is in keeping with the findings of Hadley, (9) who ad- 

 vises the study of cyst development in Coccidium in 5 per cent 



