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XIV. — On the Relation of Nerves to Odontoblasts, and on the Growth of Dentine. 

 By W. G. Aitchison Robertson, M.D., B.Sc. (With One Plate.) 



(Read 16th March 1891.) 



Clinical and pathological observation both show that the dentine of the tooth is 

 very closely connected with the nervous system, and is in consequence highly sensitive. 

 Upon what structures does the sensibility of the dentine depend ? In what manner is 

 the dentine connected with the nerves of the pulp so as to become so sensitive to external 

 stimuli ? 



Perhaps there is no other structure in the body which is so largely supplied with 

 nerves as the pulp of the tooth ; even in the smallest fragment we find many nerve fibres. 

 If we take the pulp from the incisor tooth of an ox and examine it after having allowed 

 it to lie in a solution of osmic acid for a few minutes, we can see clearly through the 

 darkened semi-transparent tissue a large blackened nerve trunk passing up the centre of 

 the pulp, giving off on its way innumerable lateral branches, and dividing in a brush- 

 like manner near the upper part of the pulp. All the fine branches are directed towards 

 the periphery of the pulp. In longitudinal sections of the pulp we can see the same in 

 greater detail ; many large bundles of medullated and non-medullated nerve fibres run- 

 ning longitudinally near the centre and giving off lateral branches, which are found in 

 great numbers near the periphery and divide into single nerve fibres just under the 

 odontoblastic layer, being specially numerous at the apex of the pulp. The separate 

 nerve fibres enter the layer of odontoblasts and are lost in it. Teased specimens of osmic 

 acid preparations of pulp also show its richness in nerves. I may note in passing that in 

 many of the teased specimens the axis cylinder of medullated fibres was often found 

 projecting a long way beyond its medullary sheath (Fig. 1). It appeared as if the 

 sheath had broken across at one of the nodes of Ranvier, and had been pulled off the 

 axis cylinder. In these fibres, however, the broken end of the sheath was sharp and 

 abrupt ; whereas had it given way at a node we should have expected to find its end in- 

 verted owing to the natural constriction in the sheath at the node. The presence of 

 these long isolated axis cylinders seems to me to completely refute the idea of Professor 

 Leydig, that the nerves are tubes filled with a semifluid substance, and also the assertion 

 of Engelmann that the axis cylinder is not perfectly continuous, but is, like the medul- 

 lary sheath, interrupted at Ranvier's nodes. 



Non-medullated nerve fibres are also seen in such preparations, though not so 

 numerous as the white. In some preparations they may be separated from the medul- 

 lated fibres and can be recognised by the nuclei at intervals in the neurilemma 

 (Fig. 2). 



VOL. XXXVI. PART II. (NO. 14). 3 D 



