PART II. CHARACTERS AND DIAGNOSIS 67 



In an absolute diagnosis of this amoeba we must rely on finding 

 the characteristic cysts, for we have no such criterion as the 

 ingestion of red blood corpuscles to guide us. 



Amoebae, however, which occur in a dysenteric stool and which do 

 not, any of them, contain red blood corpuscles are most probably 

 E. coli for the simple reason that E. coll infections are so much 

 more common in healthy individuals than E. histolytica infections. 



If amoebae show many vacuoles, especially vacuoles which are 

 large elongated almost rectangular fissures, they are probably 

 E. coli. The remarks made under E. histolytica as to the propriety 

 of waiting for a diagnosis when only, unencysted amoebae can be 

 found apply equally here, for no one in these days would advocate 



TEXT FIG. S.EnUtmceba coli with ingested cyst of E. histolytica (two-nuclear 



stage). Case Boyd, May 13, 1916. 



(See page 175.) 



treating all amoebic infections with emetin. When free amoebae 

 alone are found, the following of a case daily for a few days will 

 almost certainly reveal encysted forms. In one case only, which 

 had a persistent diarrhoea, free amoebae alone were passed for nearly 

 a fortnight before E. coli cysts appeared. 



E. coli is much more omnivorous than E. histolytica and one 

 more frequently finds bacilli, cocci, yeasts, long coiled up leptothrix 

 and unidentifiable structures within the cytoplasm. On two 

 occasions we have seen a large amoeba, almost certainly E. coli, 

 which had phagocyted a cyst of E. histolytica. A drawing of one 

 of these is reproduced (text fig. 3, above). Cysts of lamblia are also 

 ingested by E. coli. Though bacteria of all kinds are taken up 

 readily by E. coli, one sometimes finds bacteria within undoubted 

 E. histolytica. On several occasions we have noted short bright 



