98 THE AMOEBAE LIVING IN MAN 



Nowlin (1917) also found "cysts" of £. gingivalis. Their size is not 

 given, but they are said to be smaller than the active amoebae. " They 

 usually show some faint, rounded inclusions, probably the remains of 

 food vacuoles." (If this is correct, then they differ from all other amoebic 

 cysts.) The nucleus is not mentioned, and the illustration of the " cyst" 

 is very unconvincing. Mendel (19x6) maintains a judicial reserve regard- 

 ing the occurrence of cysts. I have never been able to find any cysts in 

 the mouths of persons infected with E. gingivalis. Careful search for 

 them has also been made by Smith and Barrett (1915), Goodey and 

 Wellings (1916), and Goodrich and Moseley (191^). None of them 

 succeeded in finding any, nor did Prowazek (1904). It seems to me very 

 probable that this organism does not form cysts at all, but is disseminated 

 in an unencysted condition by simple contact between mouth and 

 mouth — as Goodrich and Moseley suggest. At all events, all the "cysts " 

 hitherto found have been so imperfectly described — almost every im- 

 portant cystic character being left out of the descriptions — that it is 

 impossible to accept any of them, on the evidence so far presented, as 

 cysts of E. gingivalis. 



Craig (1916) says he has observed in E. gingivalis a process "which 

 I regard as conjugation." It is not described, however, and the observa- 

 tion is not confirmed by any other worker ; and at present there is no 

 evidence of the existence of any sexual development in this species. 

 Prowazek (1904) had previously thrown out the equally unfounded sugges- 

 tion that E. gingivalis " sporulates " in the same way as E. histolytica — as 

 erroneously described by Schaudinn (1903). 



Occnrrence and Habitat. — E. gingivalis commonly occurs in the tartar 

 of the teeth — where it was originally found by Gros (1849) — and also in 

 the materia alba between and around them. It seems to be specially 

 common in the Leptothrix masses on the inner surface. The organism is 

 often abundant in the pus found in pyorrhoeal pockets, and in other 

 oral suppurations. According to Smith, Middleton, and Barrett (19 14) 

 it also occurs in the crypts of the tonsils, and on the tongue according 

 to Lynch (1915). I have once found it among the spirochaetes and 

 fusiform bacteria in the throat of a patient with Vincent's angina. 

 Probably the organism may occur in any part of the mouth, though it 

 seems to be particularly abundant in suppurative conditions. Lynch 

 (1915) found E. gingivalis on the healthy gums and false teeth of two 

 old women who had lost all their own teeth, and who showed no signs 

 of pyorrhoea or other dental disease. 



Goodrich and Moseley (1916) have made the interesting observation 

 that an amoeba " indistinguishable " from E. gingivalis occurs in pyo- 

 rrhoeal pus from the mouths of dogs and cats. It thus appears probable 

 that the organism is not confined to man. 



Pathogenicity. — Bass and Johns (1914) and Smith and Barrett (1915) 

 originally claimed that £. gingivalis is the cause of pyorrhoea. They 

 found it almost invariably present in this condition, and constantly 

 absent from healthy mouths. Their observations, however, have not 

 been confirmed ; and almost all the recent investigators who have 

 devoted careful attention to the matter have concluded that £. gingivalis 

 is probably a harmless organism.* Observations which have been pub- 



• This is the opinion of Goodey and Wellings (1916), Goodrich and Moseley (1916), 

 and many other workers. It was also the view of Prowazek (1904). 



