ENTAMCEBA HISTOLYTICA 185 



form which produced cysts 10 to 12 microns in diameter and was pathogenic 

 to cats, and the other a less active form which produced cysts 16 to 17 

 microns in diameter and which did not give rise to infection in cats. 

 Kruse and Pasquale (1894) similarly described two forms, the one patho- 

 genic to cats and the other not. 



Though Schaudinn (1903), in his account of the amoebse of the human 

 intestine, made many erroneous statements, he was the first observer to 

 appreciate clearly the fact that two distinct species exist, the one patho- 

 genic and the other harmless. Before this, the descriptions referred 

 sometimes to the one form and sometimes to the other, and often to 

 a mixture of both. In many cases it is only the association of the amoebae 

 with pathological conditions, and their occurrence in lesions of the intestine 

 and abscess of the liver, which are now known to be due only to invasion 

 of tissues by E. histolytica, that make it almost certain that some of the 

 earlier writers were actually dealing with this form. If recent investi- 

 gations had shown that both E. coli and E. histolytica were liable to invade 

 the tissues, then there would be practically no data whatever to enable 

 a decision to be made as to which of the forms the earlier writers were 

 referring. The experiences of the past few years have demonstrated 

 clearly that E. histolytica alone is responsible for the production of patho- 

 logical conditions, so that it is perfectly clear that the amoebae described 

 in the lesions of the intestine, liver, and brain by the earlier writers were 

 actually E. histolytica, though the descriptions of the amoebse themselves 

 were in most cases so imperfect that it would be impossible to identify 

 them. Though Losch, in his original description, expressed a doubt as 

 to the part played by the amoebae in the production of dysentery, his 

 really excellent figure depicts an organism which can hardly be any other 

 than that now known as Entamoeba histolytica. 



If Schaudinn had recognized the fact that the amoeba, which Losch 

 called "Amoeba coli,'' was the pathogenic amoeba, and had given it the 

 name Entamoeba coli, endless confusion would have been avoided, but as the 

 matter stands at present there seems to be no alternative, unless further 

 confusion is to be caused, but to retain Schaudinn's name E. histolytica for 

 the pathogenic form and E. coli for the non-pathogenic one. The .whole 

 question of the nomenclature of the intestinal amoebae of man has been 

 reviewed very thoroughly by Dobell (1919), and readers are referred to his 

 book for more detailed information on this very intricate subject. 



LIFE-HISTORY. — E. histolytica is to be regarded as a tissue parasite of 

 man, as first demonstrated by Koch and Gaffky (1887), and more clearly 

 by Kartulis (1885 and 1886). Infection is brought about by the ingestion 

 of encysted forms, first seen by Quincke and Roos (1893), which have been 

 passed in the faeces of some other infected person. Under the action of 



