T. Goodev and a. W. Weldings 
553 
although common in the deposits around the teeth in this condition, 
it is by no means always present. Further, its presence in other patho¬ 
logical conditions of the oral muco-periosteum, and also under certain 
circumstances in healthy mouths does not support the claims of Smith 
and Barrett and others; but on the contrary seems to suggest that it 
is dependent upon a factor common to all these cases. That factor is, 
in our opinion, the existence of a “ trough,” or an interdental space, or 
a pocket, or a rough surface such as that afforded by an accumulation 
of tartar, or other place inaccessible to the natural cleansing agencies 
of the mouth, where food particles and cellular debris and bacteria can 
collect, and where the amoeba exercising its (in our view) beneficent 
function of scavenger of dead nuclear matter and bacteria, would find 
plenty of sustenance. 
The fact that it is not found in all such cases (see Nos. 3, 4, 7, 23 
and 24) we are not at present able to explain; possible explanations 
are: (1) The influence exerted upon the amoeba by the reaction of the 
saliva. (2) The kind of food accumulating, whether proteid or carbo¬ 
hydrate were in excess, would determine the kind of change going on 
in the accumulation, i.e. putrefactive (alkaline) or acid-production. 
(3) The variations in the mouth flora^. Cases 3 and 4 in which the 
debris collected from the tooth surfaces was strongly acid seem to sug¬ 
gest that the mouth amoeba has no great fondness for an acid medium. 
Conclusion. 
Bringing together the evidence derived from the two sources, viz. 
(1) the cytological investigation into the nature of the ingesta of the 
amoeba, and (2) the examination of a variety of oral conditions, as to 
the relation of Entamoeba gingivalis to Pyorrhoea Alveolaris, we And 
that the first leads us to the conclusion that the organism so far from 
being a destroyer of healthy tissues in the mouth is in reality a devourer 
of waste nuclear material derived from disintegrated salivary corpuscles 
together with bacteria and is therefore most probably a useful scavenger, 
whilst the second leads us to the conclusion that the amoeba may be 
found in healthy and unhealthy mouths and is especially likely to be 
found in situations where there is the possibility for the accumulation 
of food debris. 
Our general conclusion is that there is no evidence to show that 
E. gingivalis is the cause of disease. 
These of course must depend largoly upon the nature of the oral secretions and the 
character of the food. 
