24 INTESTINAL ENTAMOEBAE OF MAN 



Many free-living species are common in fresh water; com- 

 paratively few species are parasitic. Of these E. histolytica 

 (dysenteriae) is pathogenic and a very important cause of 

 dysentery, especially in tropical and subtropical countries. 



2. Species. The three important species of intestinal 

 amoebae that have been found within the intestine of man 

 are Entamoeba histolytica, E. coli, and Endolimax nana. 

 To diagnose intestinal disturbances and to, detect carriers 

 it is necessary to be able to distinguish both the motile 

 stages and the cysts of the three species. Another species 

 of Entamoeba that is of interest is E. gingivalis occuring in 

 the mouth, and accused of causing pyorrhea alveolaris. 



3. Distinguishing features. It is difficult to distinguish 

 with certainty the species of intestinal amoebae from an 

 examination of the living motile stages. The appended 

 table presents some data that may be helpful. The most 

 important diagnostic characteristics are the presence of 

 ingested blood corpuscles in E. histolytica and their absence 

 from the other species, and the distribution of the chromatin 

 within the nuclei as revealed in preparations fixed in Schau- 

 dinn's fluid and stained with iron-haemotoxylin. 



4. Distinguishing features of cysts of intestinal amoebae 

 of man. The cysts of the Amoebae of man are more impor- 

 tant from a diagnostic standpoint than the motile stages 

 since they are more easily identified and occur more fre- 

 quently in stools. Nevertheless the variation in size and 

 in nuclear number is so great that care must be taken in 

 making a hurried diagnosis and in certain cases permanent 

 preparations stained with iron haemotoxylin are advisable. 

 The accompanying table contrasts the characteristics of 

 the cysts of the three principal species. As a rule no one 

 feature is sufficient for a certain diagnosis and a combination 

 of several is desirable. 



