516 Transactions of the Society. 



fore sloped downwards towards the front. The gum at the back 

 of this tooth between it and the next molar was made to bleed by 

 slight injury and then left. Next day there was a distinctly 

 inflamed margin to the gum which appeared as a bright red rim 

 round the back and sides of this molar. Special antiseptic 

 precautions were then taken, i.e. mouth-M'ashes used as often as 

 possible. In about a week the inflammation entirely disappeared, 

 but the gum was found to have receded a little more at the back, 

 so that it was now nearly straight round the tooth. 



In the other case the gums had receded from a canine and 

 some other teeth sufiiciently to expose the crusta petrosa, and 

 after each short period of inflammation another narrow strip of 

 crusta petrosa would be exposed, and this being living bone would 

 cause great tenderness of the region for some days after the 

 inflammation had disappeared. Thus even during a week or so of 

 inflammation of the gum margin the alveolus appears to become 

 slightly reduced. Possibly this may be owing to the increased 

 number of lymphocytes in the neighbourhood, since these corpuscles 

 are said to grow into osteoclasts and other macrophages. 



Injury in such mild cases is perhaps often inflicted by the use 



EXPLANATION OF PLATES XIII^XIV, 



Fig. 5. — Extracted tooth, showing tartar ridge and gum flap which normally lies 

 closely against the tooth, with the region at which it breaks in contact 

 with the tartar. X I. 

 ,, 6. — Extracted tooth, showing by the tartar ridge that the gum had receded 

 unequally, leaving pockets — an especially deep one down one root. 

 X 1. 

 Figs. 7, 8. — Microphotographs of sections through jaws and teeth of cats with 

 advanced pyorrhoea, showing tartar detached but nearly in its normal 

 position. In fig. 7 a piece of vegetative tissue is jambed in on one 

 side. The remains of the epithelium are infiltrated with the deeply 

 staining pus-cells. The peridontal layer has become very wide. 

 The alveoli are much reduced, especially on the labial side in fig. 8, 

 and large lacunas are developing in other parts of the bone of the jaw. 

 X 11. 



Figs. 9-14. — Entamaba gingivalis. Drawn with the aid of a camera 

 lucida at an approximate magnification of 1500. 



Fig. 9. — Living form with several lobose pseudopodia, and containing seven of the 

 characteristic inclusions and a nucleus just discernible near the upper 

 end. 

 ,, 10. — Living form flattened out while feeding on bacteria, which may be seen 

 passing inwards, enclosed in vacuoles, from the left upper side. 



Figs. 11-14 from preparations stained with iron-hsematoxylin. 



Fig. 11. — Large amoeba with no visible ectosarc, and the endosarc full of various 



food vacuoles. 

 ,, 12. — SmaU form, with one large pseudopod composed of ectosarc. 

 ,, 13. — An amoeba, with two nuclei and two small lobose pseudopodia, and much 



food at various stages of digestion. 

 ,, 14. — A portioniof a section through a clump of tartar, showing amcebse between 



the terminal branches of Leptothrix. 



