THE TEETH. 



665 



"bottom of the main excavation we sometimes see a smaller cavity, it being in 

 a narrow or wide communication with the main decayed mass. 



Besides the peculiar medullary elements forming the contents of a carious 

 cavity of the enamel in its initial stage, I not very rarely have met with dark 

 "brown, irregularly shaped clusters filling the whole cavity. How such changes 

 of medullary corpuscles are produced I am unable to say, although it seems 

 to be kindred to the so-called colloid or hyaloid metamorphosis which we 

 observe in other tissues, the only difference being that in caries the colloid 

 clusters are deeply saturated with a uniform brown pigment. 



Caries of Dentine. Sometimes the dentine, attacked by caries, looks but 

 little changed on its periphery. A narrow zone of yellowish color forms the 

 boundary toward irregular, shallow excavations. At other times, besides the 

 bay-like excavations on the periphery, there are visible elongations, cylindri- 

 cal, conical, pear-shaped, or leaf-like, passing down into the dentine in vary- 

 ing depths. There is no doubt that this form of decay of the dentine occurs 

 with the least preliminary changes of the tissues ; it evidently runs a slow 

 course, and I think I am justified in calling this form of caries chronic. It 

 seems evident that decay of a tooth assumes an acute or chronic form just 

 in proportion to its perfect or imperfect calcification. Dead teeth in which 



FIG. 291. CHRONIC CARIES OF DENTINE. 



D, dentine ; O, the process of decay penetrating into the dentine in the shape of short 

 offshoots ; C, decayed mass. Magnified 200 diameters. 



the pulps have been destroyed either by necrosis as a natural process, or by 

 artificial means with caustics, very frequently run this kind of slow or chronic 

 decay. (See Fig. 291,) 



I have examined a piece of a hippopotamus tooth which for a period of 

 about one year was worn in the mouth of a patient, and a spot became 

 decayed about the size of a hemp-seed. On the bottom of the decayed pit 

 numerous conical spots appeared running downward into the dentine, 

 characterized by the absence of coloring matter in specimens stained with 

 carmine. No material change besides was observable ; even the dentinal 

 canaliculi did not look enlarged. The bottom of the carious cavity was 

 covered with a layer of finely granular, evidently disintegrated organic 

 material, and above this the ordinary masses filling carious cavities in teeth, 

 viz. : micrococci and leptothrix, were visible. 



In chronic caries first the solution of the lime-salts of the dentine takes 

 place, either along the bay-like excavations or in the shape of longitudinal 



