518 Transactions of the Society. 



Leptothrix has also been in two cases found growing and 

 forming nodules of tartar at the extreme apex of the root to which 

 there were apparently no side pockets leading. In both cases, 

 however, the crown of the tooth had been destroyed by caries, and 

 no doubt the Leptothrix had entered through the root canal. It 

 may be well to mention here that we can see no reason for separating 

 tartar into two kinds. It would be impossible to say where, e.g., 

 the line should be drawn between so-called serumal and salivary 

 tartars in the cases just described. 



We now pass on to describe some of the parasites and their 

 characteristic positions. The mouth swarms wdth all sorts of 

 organisms — Protozoa, spirochietes, yeasts, and especially bacteria 

 in incredible numbers. A great deal of work has been done on 

 these, especially the pyogenic bacteria, with a view to discovering 

 the cause of the disease ; but no particular bacterium has definitely 

 been proved to be the cause, nor do the sections of the gum show 

 any special invading organisms. 



About two years ago a sensation was caused in the United 

 States by the announcement by some Americans {1, 1'2) that the 

 amoeba of the mouth was the specific cause ; but, as we shall see, 

 further research has not supported this view. 



There is no reason to doubt that the mouth amoeba is the one 

 described and figured by Gros {6) in 1849 from the soft tartar of 

 the teeth, and it should therefore be called Entamceha (or Enda- 

 mceha) gingivalis, Gros, as has been well explained by Smith and 

 Barrett {12). It is quite a common parasite of the mouth ; even 

 young children may harbour it. Probably infection passes from 

 one person to another by direct contamination, as in kissing, using 

 the same drinking utensils, etc. We maintain that it is not to be 

 found in healthy mouths kept scrupulously clean by the use of 

 suitable antiseptic mouth-washes, etc. Nor have we so far found 

 it in healthy mouths of the few animals that we have tested, such 

 as cats, rats, rabbits, sheep and a goat. 



Its favourite habitat is the tartar, and here we come into 

 opposition with previous observers of the amoeba. It burrows, 

 not into the tissues of the gum, as has been stated, but often 

 between the terminal branches of the Leptothrix (fig. 14), and can 

 generally be found in greatest numbers on the under side of the 

 tartar ridge, where there is the greatest quantity of fresh pus. 

 From what has been said about the position of the tartar, it will 

 follow that sometimes the amoeb?e are found in great numbers 

 underneath the crown of the tooth, sometimes lower still, even at 

 the apex of a root, if the pocket should extend so far. Tw^o dogs 

 with pyorrhoea that we have examined have shown numerous 



For ExPLANATiOK OF Plate XIV, see p. 516. 



