PART II. CHARACTERS AND DIAGNOSIS 53 



which was adhering to the fur about the mouth of the first. An 

 experiment of this nature suggests very strongly that the cysts from 

 such a carrier case might give rise to acute dysentery in another 

 individual and that the same individual himself might pass into a 

 condition of acute dysentery at a later date. A reference to the 

 protocols will show that case Carr was cured by a course of 

 emetin. 



The arguments in favour of the cysts of E. histolytica being 

 actually the cysts of the pathogenic entamoeba are therefore these : 



(1) Cases which are passing cysts of E. histolytica may relapse 

 into acute dysentery when amoebae with included red blood cor- 

 puscles appear in the stool. 



(2) Cases of acute amoebic dysentery showing amoebae with 

 included red blood corpuscles may recover naturally and in the pro- 

 cess the large active amoebae become replaced by smaller forms and 

 cysts of E. histolytica. 



(3) Cases of acute amoebic dysentery of the above type may be 

 cured with emetin, but often such cases relapse when cysts of 

 E. histolytica appear in the stool. 



(4) Cysts from perfectly healthy carrier cases who have no 

 previous history of dysentery will give rise to fatal amoebic 

 dysentery in kittens. 



Taking all these points into consideration, there can be no doubt 

 that the detection of the characteristic cysts of E. histolytica in the 

 stool is in reality an indication that infection with the pathogenic 

 amoeba exists. 



(4) The History of Carriers of E. histolytica. 



Having decided that the cysts of E. histolytica are actually the 

 cysts of the pathogenic amoeba, it becomes of the utmost importance 

 to know what happens to such carrier cases, how many of them 

 actually suffer from dysentery at some time or other, how many of 

 them recover spontaneously, how long they may remain carriers 

 and what is the condition of the large intestine while they carry 

 their infections. 



(a) How long do Carriers remain infected ? This is a question 

 which only very prolonged observations can answer. In certain 

 cases, however, long histories of repeated attacks of dysentery can 

 be obtained. For instance, case Healy, who proved so resistant to 

 emetin treatment, had suffered off and on for five years and when 

 examined he was just recovering from an acute attack of dysentery, 

 and was again passing into a condition of a carrier with cysts and 



