664 



THE TEETH. 



oration, the slower is the softening process. Nay, dark-brown spots may be 

 present in the enamel for many years without being followed by softening. 

 The brown discoloration, as such, cannot be considered as an essential feature 

 of caries of enamel, but it usually accompanies the carious process, and does 

 so the surer, the slower the morbid process runs. On microscopic specimens 

 we meet with decayed pits in enamel without any discoloration of this tissue. 

 On other specimens we have a very marked orange or brown hue on the 

 decayed part as well as in its neighborhood, and sometimes scattered specks 

 .are to be seen some considerable distance from the diseased part. The brown 

 discoloration is located in the basis-substance of the enamel-rods, the outlines 

 of which are much more marked than when in a healthy condition. The 

 interstices between the rods here are plainly visible even with a magnifying 

 power of only five hundred diameters. This power will reveal delicate beaded 

 fibers of living matter within the interstices, which in healthy enamel can be 

 seen distinctly with a power of eight hundred to one thousand only. Besides 

 the discoloration, no material changes are seen on the enamel-rods. 



FIG. 290. ACUTE CARIES OF ENAMEL. 



E, unchanged enamel ; 8, enamel deprived of its lime-salts ; M, enamel broken down to 

 medullary corpuscles ; D, medullary corpuscles, indistinctly marked ; N, flat epithelia. 

 Magnified 1000 diameters. 



The process of decay in the enamel can best be studied on superficial ero- 

 sions of the same, a sample of which I have illustrated. In this instance the 

 brown discoloration of the decayed part was but trifling, and entirely absent 

 in its vicinity, so that we have to consider it as a case of acute caries. Not a 

 trace of micrococci or of leptothrix is visible in or above the decayed pit of 

 the enamel, which again proves that these organisms do not play any important 

 part in the process of caries. (See Fig. 290.) 



The shape in which caries appears in the enamel is greatly varying. Be- 

 sides the wedge shape, the forms in which caries proceeds are shallow or con- 

 ical excavations, excavations with abrupt walls, fissures, and grooves. On the 



