PART II. CHARACTERS AND DIAGNOSIS 69 



On the other band, the experiment outside the body we have 

 repeated with the small form of E. histolytica which occurs in 

 carrier cases. Though the amoebse were moving actively they did 

 not ingest the red blood corpuscles, so that it would seem that those 

 amofibsB which one finds in the stool with included red blood 

 corpuscles must be amoebae which have escaped from some definite 

 active lesion of the gut, where they have been living as tissue 

 parasites. These observations lend support to the view which we 

 have expressed elsewhere, that if amoebae are found with phagocyted 

 red blood corpuscles they are certainly E. histolytica, and are 

 taking part in some active dysenteric process, and that such cases 

 without further evidence require emetin or other anti-amoebic 

 treatment. 



Only on one single occasion, as we have noted above, has free 

 E. histolytica with included red blood corpuscles been found in an 

 ordinary unformed stool which showed no evidence of blood or 

 mucus either micro- or macroscopically. In this case there were 

 present numbers of rather small amoebae which were thought to be 

 minuta forms of E. histolytica. A search for E. histolytica cysts 

 was being made when a large active amoeba with several red blood 

 cells within it was found. No cysts were present. The case was 

 diagnosed accordingly and a few days later the diagnosis was 

 confirmed by the finding of numerous cysts of E. histolytica. 



(7) Characters and Diagnosis of Cysts of Entamceba coli. 



As regards the cysts of E. coli we have very little new informa- 

 tion to offer. We have noted, however, greater range in size 

 than has been previously admitted. James, describing E. coli, 

 has noted cysts as small as 10 microns in diameter. Undoubted 

 E. coli cysts as small as this we have not seen. The lowest limit 

 of size has been 13 or 14 microns. 



We have frequently seen infections in which practically all the 

 cysts were over 20 microns, while once the average size was well 

 over 25, and one cyst circular in outline had a diameter of 32 

 microns ; while on another occasion a cyst measuring 38 by 34 

 microns was seen. These large cysts often show sixteen instead of 

 the eight nuclei so characteristic of E. coli. It is very probable 

 that strains of E. coli exist as we have described for E. histolytica, 

 one strain differing from another in the average size of its cysts. 

 We have not, however, made any definite measurements to decide 

 this point. 



