E. histolytica: carriers 



drugs on E. histolytica in culture. The lethal dilution of 

 these drugs ranged from i to 250 for yatren casein, to 

 I to 100,000 for arsphenamine. Of particular interest 

 are the results obtained in experiments with emetin hy- 

 drochloride. Amcebse were unable to live for 24 hours in 

 culture tubes containing dilutions of i to 5000 or less 

 and were successful only at dilutions of i to 16,600 or 

 greater. At the end of 48 hours no amoebae were still liv- 

 ing in dilutions of i to 16,600 or less and only a few 

 in dilutions of from i to 20,000 to i to 100,000. The 

 size of the amoebae in cultures containing the lowest dilu- 

 tion in which they were able to exist was two or three 

 times that of normal specimens, which suggests that the 

 presence of emetin in such quantities prevents division. 

 This suggestion, that emetin in certain dilutions inhibits 

 reproduction, is also made by Dobell and Laidlaw but 

 their results show that this inhibition, if it exists, is only 

 temporary since amoebae transferred from such cultures 

 to normal cultures grow and multiply and show no ill 

 effects from their previous subjection to emetin. 



10. HOST-PARASITE ADJUSTMENTS DURING AN 

 INFECTION 



(i) The CARRIER CONDITION. Cofitact and convales- 

 cent carriers. Infections with E. histolytica seldom end 

 fatally and in most cases never exhibit an acute phase. 

 The reactions of host and parasite may result in vari- 

 ous conditions such as acute amoebiasis, the carrier con- 

 dition, latency and relapse. In the majority of cases the 

 infected host never experiences what we are accustomed 

 to consider symptoms of amoebiasis ; such a host is known 



107 



