154 HUMAN INTESTINAL PROTOZOA IN THE NEAR EAST 



(A) Emetin Hydrochloride. The cysts of E. histolytica are 

 much more resistant to this drug than are the free amoebae, for in 

 a strength of 1 in 200 (equal parts of 1 in 100 emetine and faeces 

 emulsion) it failed to kill the cysts even after nine hours' exposure. 

 It has been claimed that a strength of 1 in 100,000 will quickly kill 

 the free amoebae. 



(B} Cresol. This reagent killed all cysts immediately in a 

 strength of 1 in 20 (equal parts of 1 in 10 cresol and faeces emulsion), 

 in one minute in a strength of 1 in 30, in half an hour in a strength 

 of 1 in 100, in one hour in a strength of 1 in 200, and not at all 

 in a dilution of 1 in 2,000. 



(<7) Carbolic Acid. The cysts were all killed in fifteen minutes 

 by 1 in 40 carbolic acid, and in seven hours by 1 in 100, while a 

 1 in 200 solution failed to kill all the cysts in eight and a half hours. 



(D) Formalin. The cysts were exposed to 1 in 100 formalin. 

 Even after four hours, they did not stain with eosin, though 

 they were very much shrunken and distorted and giving every 

 appearance of having been killed. 



(E) Acid Sodium Sulphate. This drug in tablet form as used 

 for the purification of water had no action on the cysts. 



(F) Chlorinated Lime Tabloids (B. W. & Co.). This reagent as 

 used for water sterilization had no action on the cysts. The tabloid 

 gives an equivalent of one grain (0'065 gramme) of chlorine per ten 

 gallons of water (1 in 700,000).* 



From the foregoing observations it may be concluded that the 

 cysts of E. histolytica are fairly resistant structures, but are quickly 

 killed if deprived of moisture. They certainly will not withstand 

 the desiccation of a tropical sun, so that it seems improbable that 

 wind in blowing about dust can play an important part in their 

 spread. Wind, however, may distribute moist particles of faeces or 

 fragments only externally dry or even portions adhering to pieces of 

 paper or leaves. Of the few reagents we have tried cresol seems 

 the best and would be effective in a strength of 1 in 40 or 50. It is 

 important that the disinfectant should have access to the cysts, and 

 to this end the faeces must be intimately mixed with the fluid added 

 to it. Cresol can, therefore, be employed safely for the disinfection 

 of dysenteric stools, or the hands of those who have to deal with 



* In a test subsequently carried out it was found that free chlorine in water 

 at a strength of 1 in 10,000 failed to kill the cysts after several hours' exposure. 



