118 T. CHARTERS WHITE ON THE 



The intertubular tissue appears structureless. It was formerly sup- 

 posed that each tube was surrounded by a substance of greater 

 density, and described as the wall of the tube, but recent investiga- 

 tions have proved the error of this supposition. The appearances 

 to which this error may be attributed, are presented by looking at 

 a section of the dentine cut across the course of the tubes, when, 

 as a necessarily high power must be used, a small portion of the 

 interior of each tube is seen, which, being misinterpreted, was con- 

 sidered the wall of the tube. However, decalcification of the den- 

 tine reveals no wall, but it will afford an interesting evidence that 

 the tubuli are not hollow, but contain the fibrils of the odonto- 

 blastic layer, which, L if not the actual terminations of the dental 

 nerve distributed to the pulp, have, at least, a close connection with 

 it, as every one must have experienced who has had the dentine 

 excavated previously to having a carious tooth stopped. 



Now, all dentine examined under the microscope will not present 

 the regular characters I have attempted here to describe. Instead 

 of being regular and homogeneous in its character, it will appear as 

 a mass of unfused globules — what is known as globular dentine — 

 and it is a sign that the tooth has been imperfectly calcified ; such 

 teeth commonly have the enamel honeycombed and ridgy, and its 

 prisms imperfectly joined, the teeth being very sensitive to all 

 irritants applied to them, and prone to early decay. Another 

 abnormal appearance manifesting itself in the dentine, and with 

 which all observers should be familiar, is that known as osteo-den- 

 tine or secondary dentine. It usually presents itself to notice in 

 teeth that have been subject to much wearing away of the crown, 

 by which the enamel is ground away, exposing the sensitive den- 

 tine beneath, and so producing that exciting cause which I have 

 just now said the odontoblasts wanted to wake them up to their 

 suspended function. Again, when decay attacks a tooth, and the 

 cavity has reached the dentine, its first effect is to irritate the fibres 

 contained in the dentinal tubuli, and these become consolidated 

 round the point of attack, probably by a calcification of the fibres, 

 but advancing caries soon reaches the barricade, when a second is 

 thrown up by a similar calcification, but barrier after bai'rier is set 

 up and overthrown ; at last the odontoblasts themselves take on 

 activity, and fresh dentine, but of a very disturbed and irregular 

 character, is deposited on the walls of the pulp-cavity, in front of 

 the advancing foe. 



