THE DENTAL PULP 229 



visible in preparations which have been made by the Koch- 

 Weil balsam process, but is also seen in many decalcified 

 sections. 



With low powers of the microscope no distinct structure 

 is visible in this area, but with higher powers it is seen 

 to be occupied by an interlacement of delicate fibres. Weil 

 compared this layer to a basement membrane, looking upon 

 the odontoblasts as being analogous to a layer of epithelial 

 cells, but there is very little evidence to support any such 

 view, and the actual structure of this layer can, we think, 

 be quite clearly demonstrated. 



The denser connective tissue of the pulp extends in this 

 position as an interlacement of delicate connective-tissue 

 fibres which pass between the odontoblasts to the dentine, 

 and there become incorporated in the matrix, but the same 

 area is also occupied by the plexus of fine nerve fibres 

 beneath the odontoblasts which communicate with nerve 

 ' end cells ' within the odontoblast layer. It is also crossed 

 by the pulp processes of the odontoblasts, which are usually 

 delicate and not very evident in many preparations. In 

 order to show that this so-called layer of Weil was not 

 a clear space, but occupied by fibres which do not stain by 

 ordinary methods, the author removed the balsam from 

 a Weil preparation which showed the area very distinctly, 

 by soaking it in chloroform. The section was then restained 

 with gold, reduced by the Beckwith process ; the clear 

 layer was no longer visible, being entirely occupied by 

 a dense plexus of delicate nerve fibres forming the deep 

 plexus, or plexus of Raschkow, the delicate connective-tissue 

 fibres remaining unstained. 



The plexus of Raschkow is much more evident in some 

 parts of the pulp than in others, and this is also noticeable 

 with regard to the basal layer. It is not seen at the root 

 end of the tooth where the nerve plexus is also absent, and 

 at the coronal portion where the nerve fibres from the divid- 

 ing medullated trunks pass more directly to the odontoblast 

 layer this area described by Weil cannot be detected. 



Von Ebner and Rose doubted its existence as a distinct 

 structure and considered it was artificially produced, but 

 that this rarified area of the pulp tissue is present in many 



