Page 202 - My FlipBook

176 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

Tliis is intended to represent a case of undermining decay on
tlie enamel lias been broken
the grinding-surface of a molar ;
througli, and tlie softening (decalcification) lias extended in all
directions in the dentine with about equal rapidity. The micro-
organisms, on the other hand, travel more readily in the direc-
tion of the dentinal tubules than at right angles to them, since
in the latter direction they can advance only through the tortu-
ous and narrow road of the fine branches of the tubuli. Conse-
quently, while the micro-organisms almost or quite keep up with

Fig. 69.

A Cut from a Large Piece of Decayed Dentine, left half only in outline. Shows at a an
unusually large non-infected zone of decayed dentine. 20 : 1.
the softening in the direction toward the pulp, they fall consid-
erably behind in the lateral directions, so that the invasion, par-
ticularly in the lateral direction, is usually much less extensive
than the softening.
Fig. 69 represents the appearance under a low power of a
preparation of decayed dentine in my possession.
Cases where there are many large interglobular spaces may
form an exception to the rule. In such cases, the bacteria, fol-
lowing the course of the interglobular spaces, can advance very