PART II. CHARACTERS AND DIAGNOSIS 43 



to show how impossible it is at times to arrive at a diagnosis of the 

 amoebae themselves and how important it is to take into considera- 

 tion other features of the cases in which they occur. 



Realizing the practical difficulties standing in the way of 

 accurate diagnosis we have fixed a very definite standard for our 

 present series of observations a standard which one of us has 

 upheld and taught for a considerable time in connection with this 

 work and one which the ordinary observer, who knows how to 

 recognize amoebae and cysts, can readily follow, We have called 

 no infection one of E. histolytica unless' we have found at least 

 some amoebae with included red blood corpuscles present, or unless 

 we could find definite cysts of E. histolytica associated with the 

 amoebae in the stool. It has happened on many occasions that 

 amoebae have been found in dysenteric and diarrhceic stools which 

 may or may not have been E. histolytica, but unless some of the 

 amoebae contained red blood corpuscles, or unless encysted forms 

 were present, we have left the diagnosis at " free entamoebae " alone 

 and have followed the cases for several days after the preliminary 

 examinations. Such cases watched from day to day in most 

 instances show cysts of E. coll alone in the stool as the symptoms 

 subside, while in a smaller percentage of cases E. histolytica cysts 

 appear. In practically all cases in which amoebae of doubtful 

 nature occur an observation extending over a few days will clear up 

 the diagnosis as cysts make their appearance. There are, however, 

 very rare exceptions to this rule of the appearance of cystsy-as has 

 been noted by James in certain cases in Panama. This observer 

 followed three cases of untreated amoebic dysentery for three weeks 

 and no tendency to cyst formation occurred. One of our cases, 

 however, has been watched for over three months, the stool being 

 examined practically every day, and though the case is undoubtedly 

 one of amoebic dysentery as active amoebae containing red blood 

 corpuscles have been present from time to time during typical 

 attacks of dysentery, on no occasion have cysts of E. histolytica 

 appeared. This case has been treated with emetin on several 

 occasions but has always relapsed sooner or later with a return of 

 the dysenteric symptoms. As a rule, however, cysts occur at some 

 time in the course of infections. For instance, in the case of 

 Russell, H., who was admitted with amoebic dysentery, there was 

 blood and mucus in the stool with active amoebae containing red 

 blood corpuscles. The case was given a twelve-day course of emetin 

 (one and a half grains a day by the mouth and injection) and 

 the symptoms and infection cleared up. A week later cysts of 



