250 FAMILY: AMCEBID^. 



in cases studied by them. Kofoid (1923), however, describes spherical 

 cysts of this amoeba containing one or two nuclei and one or more vacuoles. 



In a case seen by the writer, in which E. histolytica as well as 

 D.ffagilis occurred, both infections disappeared after a course of emetine. 



Thomson and Robertson (1925) report the successful culture of 

 D. fragilis in the medium used by Boeck and Drbohlav for the culture 

 of E. histolytica. 



DIAGNOSIS OF THE INTESTINAL AMCEBiE OF MAN. 



In order to arrive at a conclusion regarding the nature of the amoebae 

 or their cysts which are found in human faeces, very careful, and sometimes 

 prolonged, examinations are necessary. It must always be remembered 

 that mixed infections are common, so that it is never possible to be 

 absolutely certain that all the amoebae present have been diagnosed. In 

 the case of malaria there may be found a large infection of ring forms 

 about the nature of which there may be considerable doubt. Search may 

 reveal a few crescents, and though it will then be known that Plasmodiiitn 

 falciparii?n is present, it will still be impossible to assert that all the rings 

 belong to this species. Similarly, with the amoebae there may be a mixture 

 of free forms of E. coli and E. histolytica, and the discovery of the charac- 

 teristic cyst of one species does not exclude the possibility of some of the 

 free forms belonging to the other (Fig. 117). 



Examinations repeated on several different occasions reduce this error 

 to a minimum, but cannot entirely eliminate it. It was demonstrated 

 by the writer and O'Connor (1917) in a series of cases that the positive 

 findings which result from the examination of the first specimen yield 

 only one-third of the positive results obtained by examinations repeated 

 on a number of successive days. Very often it may be impossible to 

 determine the nature of the free amoebae in any specimen. The large 

 forms may be E. coli or E. histolytica. The intermediate forms may 

 be either of these or /. hutschlii, while the small forms may be any 

 of these or E. nana or D. fragilis. The precystic forms of E. coli 

 and E. histolytica may be difficult to distinguish from one another. 

 Diagnosis is most easily made by finding the cysts in saline or iodine 

 preparations, if not on one day, then on another. If cases are examined 

 repeatedly, encysted forms will generally be found (Plate II., p. 250). 



As regards the large amoebae from 15 to 20 microns or more, if they 

 occur in dysenteric stools and are very active, they are probably E. histo- 

 lytica. If so, the nucleus should be difficult to see, and search may reveal 

 forms including red blood-corpuscles. In the latter case the amoebae 

 are certainly E. histolytica. E. coli may, however, be present in dysenteric 



