OF THE ALIMENTARY TRACT 51 



thirty minutes but are killed within five minutes at 

 50°C. Ordinary chlorination of water, such as is 

 commonly used in public water purification was with- 

 out effect upon them but they were fairly sensitive 

 to bichloride of mercury (1 to 2500), formaldehyde 

 (0.5%), carbolic acid (1.0%) and lysol (1.0%). 

 Boeck (1921), using eosin absorption as a test of the 

 viability of cysts, indicated that this phase of End- 

 amoeba histolytica survives for months in plain 

 water. 



Whether either of these methods, and which the 

 better, suffices to determine when protozoan cysts 

 are no longer able to hatch living organisms in the 

 intestine remains to be conclusively shown. 



Stools, water, and other liquids and moist materials 

 containing Endamoeba histolytica cysts may be con- 

 sidered infectious for some time at least. Contam- 

 inated water is not freed of its infectiousness during 

 this time by ordinary chlorination. The heating of 

 foods which may have been exposed to contamination 

 to 55°-60°C., the pasteurization of milk, similar 

 heating or boiling of drinking water, should control 

 the dissemination of the infection, where proper sew- 

 age disposal is not done, except the hand-to-mouth 

 carrier transmission. When proper sewage disposal 

 is not available, fecal matter should be disinfected 

 by an agent of known amoebicidal properties (Craig 

 [1926] recommends mixing the stool in cresol 1 to 200 

 for 15 n>inutes) and fly control and screening should 

 be carefully exercised. Where human excreta is used 



