ENTAMOEBA GINGIVALIS 95 



research will demonstrate that still other species of amoebae occur in 

 the human mouth " ; and he adds " it will be strange indeed if both 

 Endauweba histolytica and Endaiiioeba coli, the common intestinal end- 

 amoebae of man, are not sometimes encountered in this locality." This 

 last statement appears to me to be a wild and wholly unwarranted pre- 

 diction, which, if fulfilled, will indeed be strange. It will, indeed, 

 be more — it will revolutionize our present conceptions not only of the 

 amoebae but also of parasites generally. For the moment, however, 

 there is no evidence whatever to support Craig's view, and there is very 

 little in favom^ of the hypothesis that more than one species of amoeba 

 inhabits the mouth of man. 



Description. 



Entamoeba gingivalis is a small amoeba which appears to show great 

 variation in size. Provvazek (1904) gives its diameter as 6-32 yu. ; 

 Chiavaro (1914) gives 5-20 fi ; Mendel (1916) gives 5-40 /a ; Goodey and 

 Wellings (1916) give 7'5-27 /i ; Goodrich and Mosely (1916) 10-30 /^ ; 

 and Nowlin (1917 a) 12-40 /x ; whilst Smith and Barrett (1915) state that 

 the usual diameter is 30-35 /m, and that organisms may measure even 

 more — up to 60 /x,. In my experience this amoeba is usually much 

 smaller, and its diameter is usually between 10 fi and 20 fx in fixed and 

 stained specimens. I have not seen living organisms with a greater 

 diameter than 25 fi, and as a rule they have been considerably less. 

 My impression is that this species is typically smaller than E. coli, but 

 I have studied only a limited amount of material. 



The organism when alive resembles E. coli in general appearance, 

 but is usually more active. Ectoplasm and endoplasm are fairly sharply 

 differentiated, and the pseudopodia are well-developed, lobose, and 

 typically rounded — not pointed. Individuals showing their pseudopodia 

 extended are much more frequently seen in stained preparations of this 

 species than in those containing E. coli or any of the other intestinal 

 amoebae of man — all of which tend to become spherical when fixed. 

 The most striking feature of the living amoeba is its cytoplasm, which 

 is usually filled with numerous food vacuoles containing peculiar in- 

 clusions. In this respect it often resembles a well-fed small individual 

 of E. coli. The nature of these inclusions will be considered later, but 

 it should be noted here that they have a greenish, refractile appearance, 

 and are roundish in shape, so that they are not unlike ingested red 

 corpuscles seen with ill-adjusted illumination. Red corpuscles are, 

 however, in my experience, invariably absent from the endoplasm. 



The nucleus of E. gingivalis is typically spherical and vesicular, 

 inconspicuous during life, and closely resembles those of E. coli and 

 E. histolytica in structure. (See PI. V, figs. 93, 94.) Its diameter in my 

 stained specimens is generally from 2'5 /* to 3 /i, and it appears to be 

 slightly smaller, relatively to the diameter of the organism, than the 

 nucleus of E. histolytica or E. coli. The size is variously given by 

 different observers as 2-5-4 /* (Goodey and Wellings, 1916), 2-5 /a (Smith 

 and Barrett, 1915), or 3-6 fj, (Goodrich and Moseley, 1916). There is 

 probably a very thin achromatic membrane surrounding the whole 

 nucleus, as in other Entanwebae. As a rule this is invisible, however, 

 and the chromatin granules which are massed against its inner surface 

 completely hide it. These granules are, in healthy and well-fixed 



