224 FAMILY: AM(EBID.E 



Kofoid and Swezy (1924a) maintain that all descriptions of the nucleus 

 hitherto given are inaccurate, and that definite differences not previously 

 noted distinguish it from the nucleus of E. histolytica. They state that 

 the karyosome is not always a single granule, as in E. histolytica, but is 

 often composed of a group of granules, and that the halo round the karyo- 

 some is granular and large, in contrast with the clear and relatively smaller 

 halo of E. histolytica ; furthermore, the intermediate zone between the 

 nuclear membrane and halo is clear in E. gingivalis and granular in 

 E. histolytica, while in the former the chromatin is less regularly arranged 

 and more liable to clumping on the nuclear membrane. Whether such 

 minute differences are sufficiently constant to justify the determination of 

 species future investigations alone will show. 



Reproduction of E. gingivalis probably takes place by binary fission, 

 and the binucleate forms occasionally seen must represent a stage in this 

 process. The division has never been followed in detail. 



Craig (1916) has recorded the finding of cysts, but it is evident from 

 his figures that the structures described were not cysts at all. Similarly, 

 Smith and Barrett (1915), and Nowlin (1917), described as cysts structures 

 which were more than doubtful. The writer has examined E. gingivalis 

 on many occasions, but was never able to discover encysted forms. This 

 has been the experience of Dobell (1919), Kofoid and Swezy (1924a), 

 and other workers. It is probable that cysts occur, but if they have 

 ever been seen, no convincing description has yet been given. 



E. gingivalis can easily be studied in material obtained from carious 

 teeth or in pus squeezed from pyorrhoeal pockets. In the writer's ex- 

 perience the amoebae sometimes appear to be absent in particularly foul 

 mouths when they might be expected to be present, while on other occa- 

 sions they have been found in the mouths of people who are very particular 

 as to their dental toilet. 



Attempts to infect animals with E. gingivalis have not been successful. 

 Goodrich and Moseley (1916) have noted that an organism indistinguish- 

 able from E. gingivalis may be found in pyorrhoeic conditions in dogs, 

 while Nieschulz (1924c) has described as E. gingivalis var. equi a similar 

 form from the accumulations round the teeth of horses, 



Tibaldi (1920) has recorded the discovery of E. gingivalis in the human 

 tonsil. He has also described as E. macrohyalina an amoeba of 

 another type which he has found in two cases of tonsillitis. This amoeba 

 is considerably larger than E. gingivalis, and may reach a diameter of 

 40 microns. It has, moreover, a well-marked ectoplasm and a different 

 type of nucleus, though it must be admitted the figures given suggest 

 a faulty fixation. It is possible, as noted by the writer (1922a), that 

 E. gingivalis, which usually lives as a saprophyte, may become modified 



