PART II. CHARACTERS AND DIAGNOSIS 71 



written that the distinctions between E. coli and E. histolytica 

 will not hold. We quite admit the difficulty of distinguishing 

 vegetative forms of the amoeba*, and recognize that occasionally 

 there may be some uncertainty even with the cysts, for large 

 strains of E. histolytica cysts occur as well as small strains of 

 E. coli. E. coli cysts may have chromidial bodies, but the 

 presence of four nuclei in the fully developed E. histolytica cysts 

 is so universal that one can state with certainty that this is a 

 reliable feature for diagnostic purposes. The E. coli cysts when 

 developed have eight nuclei, and sometimes more. The clearest 

 demonstration of the difference of the two cysts is seen in cases of 

 mixed infections treated with emetin where the E. coli cysts 

 survive the treatment, and the smaller four-nuclear E. histolytica 

 cysts disappear ; while in pure E. histolytica infections there is a 

 complete disappearance of all the cysts. Such cases are absolutely 

 impossible to explain on any other basis than that the two amoebee, 

 E. coli and E. histolytica, represent two distinct species of different 

 characters and habits. 



(8) The Course of E. coli Infections. 



It has already been pointed out by one of us (C. M. W.) that 

 E. coli infections may persist for several years. James, working in 

 Panama, mentions a case which constantly showed E. coli during 

 a period of about five years. A case of E. coli infection which was 

 not complicated by the presence of any other protozoon we have 

 followed very carefully during the last few months. The results of 

 the examinations made during a period of 120 days are shown 

 in the accompanying table (page 72). The character of the stool at 

 each examination and the occasions on which a saline purge was 

 administered are set down, for it will be seen how directly this 

 affects the finding. Encysted forms were present on most occasions, 

 whereas the free unencysted forms were rarely present except when 

 the stool was soft after the saline purge. On the ninety-fifth and 

 ninety-sixth days there was diarrhoaa accompanied by a very large 

 blastocystis infection. This case illustrates very well what may be 

 taken as the normal course of an' E. coli infection judged by the 

 appearances in the stool. This case also had an ankylostoma 

 infection and the days on which eggs of this worm were present 

 are shown in a separate column. 



On the ninety-fifth and ninety-sixth days there was an attack of 

 unknown origin. At this time blastocystis, which had been present 



