322 DR W. G. AITCHISON ROBERTSON ON THE RELATION OF 



How do these terminal filaments of the nerves end in the odontoblastic layer ? Why 

 should there be such a multitude of nerves in the pulp if they have not a special function 

 and definite termination ? In all other parts of the body, the function of nerves is motor 

 or inhibitory, sensory, secretory, or trophic, and the fibres mostly end in special ter- 

 minal structures at the periphery. Do the nerves of the tooth end in the odontoblasts 

 themselves ; or, as Magitot affirms, in a layer of cells beneath the odontoblasts ? Do 

 they pass between the odontoblasts and accompany the dentinal fibres into the dentinal 

 tubules as stated by Waldeyer ; or do they pass between the odontoblasts and occupy a 

 special set of tubules in the dentine, as described by Boll ? To find the true answer to 

 these questions was the object of this rather difficult inquiry, and the conclusions I have 

 arrived at I will now detail. 



I shall in the first place describe the odontoblasts as I have seen them in the pulp of 

 the ox tooth. On examining the microscopic sections of the pulp I was surprised to find 

 odontoblasts were absent from their periphery. At first I thought they had merely 

 fallen away during the process of mounting, but their absence was so constant that 

 another explanation had to be sought. At first I fractured the tooth with a hammer, 

 and on separating the fragments, the pulp was usually found lying almost free. These 

 were the pulps which showed an entire absence of odontoblasts when cut into sections. 

 Professor Haycraft one day happened to pick up a fragment of the tooth thus fractured, 

 and noticed on its inner surface a shining membrane. This when examined was found to 

 consist of many cells, often closely aggregated, and having a round, oval or pyriform shape 

 (Fig. 3). Attached to many of the oval cells there was a long process embedded amongst 

 the other cells. Other fusiform or tailed cells lay free, each having a large nucleus situated 

 in the centre of the round or oval cells, and at the broad end of the pyriform cells. These 

 were the odontoblasts that were missing in the sections. The greater number had remained 

 attached to the dentine when the pulp was separated, showing that their connection with 

 the dentine is stronger than with the pulp which they invest, and also demonstrating 

 the actual existence of the membrana eboris of Kolliker. The tail or elongated process 

 of these cells is not the dentinal fibre, for it is directed into the substance of the pulp, 

 but is the root, central, or pulp process of the odontoblast. The dentinal fibre or 

 peripheral process had been torn off the greater number of the odontoblasts by the act 

 of scraping, though in many a small stump of it remained attached to the opposite ex- 

 tremity of the cell, and in some cases this proximal part of the dentinal fibre could be 

 seen entering a dentinal tubule. These two processes, the long pulp process and the 

 dentinal fibre, are the only processes in the odontoblasts of the ox. These cells have no 

 lateral processes. 



To see the odontoblasts in situ I sawed through some teeth with great care and 

 removed the pulp by means of a sharp knife. I made sections of these pulps after em- 

 bedding in paraffin, and found that although not all, yet a very large proportion of 

 odontoblasts remained attached to the pulp. These were seen to be arranged in two 

 layers. Many dentinal fibres could be seen projecting from the periphery of the pulp to 



