ENTAMOEBA GINGIVALIS 99 



lished by Lynch (1915), Mendel (1916), Goodey and Wellings (1916), 

 Goodrich and Moseley (1916), Williams, ShoUy, Rosenberg, and Mann 

 (1915), Mitchell, Culpepper, and Ayer (1916), and others, show conclu- 

 sively that E. giiigivalis occurs in normal healthy mouths. For example, 

 Mitchell, Culpepper, and Ayer say : " it is evident that a very large per 

 cent of normal mouths harbour " this organism. They found amoebae 

 in the mouths of 2i'6 per cent, of children with normal gums ; and 

 Mendel found them in 8 out of 36 children, and in 24 out of 42 adults, 

 all of whom showed no evidence of pyorrhoea. It seems equally certain, 

 on the other hand, that E. gingivalis occurs more abundantly in the 

 mouths of persons with pyorrhoea and unhealthy gums. Thus, Mendel 

 (1916) found the organism in 38 out of 40 persons with pyorrhoea; 

 Williams, Sholly, Rosenberg, and Mann (1915) found them in 70 per 

 cent, of children with "spongy, bleeding gums"; and Mitchell, 

 Culpepper, and Ayer (1916) found them in 74-4 per cent, of children with 

 " receding, spongy, bleeding gums." As £. gingivalis feeds largely upon 

 bacteria and the nuclei of disintegrated cells in the saliva, it seems not 

 improbable that a condition such as pyorrhoea — with abundance of 

 bacteria and broken-down pus cells — is particularly favourable to their 

 growth. This would easily account for the greater frequency of the 

 amoebae in suppurative conditions. 



E. gingivalis is by no means always present in pyorrhoeal pus, or in 

 dental abscesses. I have examined at least one case of pyorrhoea, and 

 the pus from two dental abscesses, with completely negative results after 

 a very exhaustive search. Similar results have been recorded by others. 

 The heaviest infection which I have seen was in a man with only 

 slight pyorrhoea, but with a very dirty and ill-kept mouth. Scrapings 

 from all parts of the teeth and gums showed large numbers of amoebae, 

 often accompanied by Trichonionas and immense numbers of spiro- 

 chaetes. I have also seen E. gingivalis on one occasion in a syphilitic 

 lesion of the mouth — a mucous patch on the lower lip. 



Hecker (1916) attempted to cause pyorrhoea by \n]tcimg E. gingivalis 

 — washed by a special technique, to free the amoebae from bacteria — 

 into the gums of a guinea-pig and a man. Repeated inoculations did 

 not succeed in establishing an infection or in causing pyorrhoea. 

 Pro wazek (1904) found E. gingivalis in carious teeth, but the observa- 

 tions of Chiavaro (1914) and Mendel (1916 a) seem to show that dental 

 caries is not caused by its presence, as some writers have suggested. 



At present, therefore, there seems to be no good evidence to support 

 the hypotheses that E. gingivalis attacks the tissues, that it is the cause 

 of pyorrhoea, or that it is in any way pathogenic. The suggestion that 

 the amoeba acts as a pathogenic agent by means of a " symbiotic rela- 

 tion " with certain bacteria, as suggested by Smith, Middleton, and 

 Barrett (1914), seems equally unfounded. The organism appears rather to 

 be a harmless commensal, like E. coli. Chiavaro (1914) considers that it 

 is " most probably an adjuvant in the autodisinfection of the mouth;" 

 whilst Goodey and Wellings (1916) suggest that, since E. gingivalis is a 

 "scavenger" of bacteria, it "may therefore be considered as a useful 

 rather than a harmful organism." The available evidence, however, 

 appears to me to afford but little ground for regarding it as either harm- 

 ful or beneficial. 



Trealment. — As already noted, Bass and Johns (1914, 1915), Smith, 

 Middleton, and Barrett (1914). Lynch (1915), and others, claimed to 



