1070 PATHOGENIC PROTOZOA 



in connection with some other amoeba and never alone, but it is 

 not believed that they have any pathological importance. 



Until recently the vegetative stage had not been recognized, but 

 in 1919 Dobell published a complete description, and identified the 

 parasite with the one incompletely described by Prowazek as En- 

 tamoeba biitschlii in 1912. 



In size the organism is small, averaging 9 to 13 microns, and it 

 resembles E. coli in general appearance except that the nucleus is 

 almost if not quite invisible, particularly in organisms with food 

 vacuoles filled with bacteria and granular matter. 



In stained specimens the structure of the nucleus serves to dis- 

 tinguish it from other intestinal amoebae. The nucleus is vesicular 

 and contains a relatively large karyosome, one-third to one-half the 

 diameter of the nucleus. Between the karyosome and the well 

 developed nuclear membrane lies a row of granules of peripheral 

 chromatin which Dobell has succeeded in counterstaining with eosin 

 in well differentiated hematoxlyn preparations. It is the presence 

 of this large karyosome and the layer of peripheral chromatin dots 

 that permit the differentiation of the organism from E. coli; the 

 two organisms are alike in their food habits. 



The cysts are peculiar and quite unlike those of any other 

 intestinal amcebas. In shape they are irregular although some are 

 round or oval. In measuring them Dobell averaged the two prin- 

 cipal dimensions and found that the average size is 9 or 10 microns, 

 with extreme of 6 to 16 microns. The nucleus of the cysts is single, 

 and is distinguished by having the karyosome, which has already 

 been described, pass to the periphery and come to rest against the 

 nuclear membrane, giving rise to a well marked signet ring appear- 

 ance. Peripheral granules of chromatin may still be made out in 

 well stained specimens. Occasional cysts may have two nuclei but 

 they may be interpreted in the same way that we interpret more 

 than the usual number of nuclei in E. histolytica and coli, as an 

 abnormality. 



The iodin masses in the cysts which give this organism its name 

 are well brought out by staining the fresh specimens in iodin solu- 

 tion. As a rule the glycogen mass is single, large and has well 

 defined borders, but its appearance varies with its age ; the precystic 

 amoeba shows merely a diffuse brown stain, older specimens appear 

 as above, although occasional specimens may show more than one 

 iodin staining mass. Throughout the cytoplasm may be seen granules 



