On Certain Parasites of the Mouth in Cases of Pyorrhoea. 523 



branching of the Leptothrix threads. The radiating bundles of 

 relatively coarse threads divide and subdivide before reaching the 

 periphery of the colony and may finally end in a few threads. 

 These may project far beyond the general surface of the colony, 

 and, being usually covered with coccoid forms, and finer and shorter 

 threads set more or less at right angles to this axis, form a terminal 

 branch, one of the many of very variable form with which the 

 whole surface of the colony is thickly beset. The coccoid forms 

 on the branches appear to be set in rows radiating from the axial 

 threads. This arrangement is well seen in specimens of branches 

 stained with Stephens' ink. In the solid mass or groundwork of 

 the colony, however, their arrangement cannot be made out. 

 Threads of Leptotlirix often show terminal swellings or " clubs," 

 both inside the colony and at the periphery. These are very prone 

 to calcify (fig. 19). 



Where a colony is growing on the surface of a tooth or other 

 attachment it is of course modified in shape, but the bundles of 

 coarse iodine-reacting threads always radiate from the centre of 

 attachment, and there the hard tartar is deposited, chiefly by the 

 progressive calcification of these threads, and is thus built up 

 layer by layer as the colony grows and spreads. The forms of 

 Leptothrix colonies vary considerably according to their position 

 in the mouth. Those most branching and diverse are met with 

 usually where the tartar ridge meets the surface of the gum-flap. 

 Colonies situated above the surface of the gum margin, slightly 

 higher up on the tooth, have usually less complicated branches. 

 A variety frequently found on colonies in this position has been 

 described as " flowering heads " by various writers (fig. 20). They 

 are well illustrated in two microphotographs by Leon Williams {lo), 

 reproduced by Goadby (-5). The young colonies found scattered 

 over the surface of the tongue (fig. 17), and radiating from a core 

 of a few dead epithelial cells, are often entirely composed of coccoid 

 forms, these coccoid forms being set in regular rows, with alternating 

 areas of finer or coarser granules, all apparently radiating from 

 their centre of growth. The Leptothrix also flourishes on the surface 

 of decaying dentine, its threads radiating from the decayed surface, 

 and as a rule very little or no tartar is deposited when it is gi'ovving 

 in this position. The Leptothrix also grows on foreign bodies in 

 the mouth ; thus we have found it growing abundantly on a 

 fish-vertebra which had become lodged between two teeth in a cat. 

 It has also been described by Leber and Eotten stein {8) growing 

 on substituted human teeth, with decalcification taking place in 

 exactly the same way as in ordinary caries. Under certain 

 conditions as yet unascertained * the Leptothrix colonies develop 



* We have not found this kind of branch on perfectly healthy extracted teeth 

 or in healthy mouths. We always find it on extracted teeth from advanced cases 

 of pyorrhcsa. It usually abounds in pyorrhoea pockets. 



