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Rh If a tooth be removed from its capsule, and macerated for some days in slightly diluted hydrochloric acid, the dental substance, which on the first withdrawal of the calcareous salts possessed a cartilaginous consistence, becomes so very soft that it can only be removed from the acid in very small portions with the forceps. This pappy mass is found on examination to consist of fibres, which may here and there be insulated. (See pl. III, fig. 5.) These fibres are too thick to be the walls of the tubes; they form the entire substance. Nor can they well be an artificial product, the result of the acid penetrating into the tubes, and dissolving, in the first instance, the substance in immediate contact with them, so that the intercellular substance remained undissolved in the form of a fibre; they are too regular and smooth for that. It appears rather that the dental substance is composed of these fibres, which have become blended together, that they are therefore identical with those fibres, by the coalescence of which, according to Purkinje and Raschkow, the dental cartilage is formed, and that this coalescence is not so complete, but that it may be artificially dissolved. The fibres have the same course as the tubes in human teeth, but I could no longer perceive the tubes between them in this preparation; I could, however, recognize the fibres everywhere, save in the most external layers which lay immediately under the enamel, in which situation the mass was more completely broken down by the acid, and traversed by more minute fibres of a different kind, having the most confused and varied directions, and which I suppose to have been the remains of the dental tubes.

We must therefore regard the dental substance as composed of fibres blended together, between which run tubes provided with special walls. The fibres and tubes are nearly perpendicular to the dental cavity in human teeth. What connexion now is there between the fibres, or the tubes, and cells? I should incline to the old opinion, that the dental substance is the ossified pulp. According to Purkinje and Raschkow, the pulp in the first instance consists of globules, of nearly uniform appearance, but has neither vesselsnor nerves. At a subsequent period vessels appear in it, and afterwards nerves. Upon the surface of the pulp, the globules are more regularly arranged, and more extended in the longitudinal direction,