ON A PECULIAR SUBSTANCE OCCURRING ON THE HUMAN TEETH. 67 



terminate in a point. They are smooth, of a yellowish white, somewhat 

 transparent, are elegantly curved or wavy ; or, when they occur in the 

 second form, are occasionally quite straight, and apparently stiff. Their 

 elasticity however admits of no doubt, as in moving the plates of glass, 

 they frequently turned and moved in various directions. Professor Va- 

 lentin believes also that their surface is not granular, and their margin 

 not varicose ; although it sometimes had that appearance, as small mole- 

 cules attached themselves to the surface, which did not belong to the 

 constituent, but to the adhering portions of the form, as was plainly 

 observable if the object was well in focus. Professor Gerber, however, 

 has observed both these peculiarities. Farther and more complete inves- 

 tigations will probably decide this point. I never saw these fibres rup- 

 tured, yet broken parts are occasionally to be seen in the second form. 

 Single fragments of these fibres, which are cylindrical and have a broad 

 end on each side, may be perceived. The point of fracture is straight, 

 and exhibits no protruding portions. As regards the occurrence of these 

 forms, I have found that they exist only on the teeth, but not on the 

 slime ; that they occur both in young and old individuals, but more fre- 

 quently and more abundantly in the case of older persons, who usually 

 pay less attention to their teeth, which on this account are coated with 

 slime and tartar. They then display themselves chiefly in the form of 

 Nos. 2 and 3 equally on all the teeth. I have looked for them on my 

 own teeth, after having first very carefully cleaned them with a brush, 

 and have found them again. They are most numerous when a portion 

 of slime lies between the teeth, and particularly towards the bases of the 

 last teeth, As regards their chemical composition, I can only state at 

 present, that acids leave this peculiar substance totally unaltered, or at 

 most, only render it somewhat more transparent. The strongest nitric, 

 sulphuric, or muriatic acids do not dissolve it. The most concentrated 

 solution of caustic alkali produces no alteration of form. If consumed 

 on a plate of glass, in a platinum crucible, the surrounding mass is 

 changed into carbon, but these fibres remain unaltered. This however 

 is only to be observed as regards those which exist on the margin of the 

 blackened mass ; the others, though certainly not consumed, are mecha- 

 nically inclosed in the black substance, and therefore cannot be discerned 

 with the microscope. 



I beg to submit this sketch as a mere preliminary notice on the sub- 

 ject, in order that other and more competent observers may devote their 

 attention to these objects, hoping myself to be able to communicate 

 more complete information at a future period. 



F2 



