114 T. CHARTERS WHITE ON THE 



Now, as the dental pulp at this time is busily engaged in the 

 formation of the most important tissue in the tooth, I must ask 

 your attention to such a short description of its histological 

 characters as may enable you the more readily to comprehend the 

 hard tissue which immediately results from its agency. The tooth 

 germ, or dental papilla, corresponds in form to the future tooth, 

 and is richly supplied with nerves and blood-vessels, the vessels 

 being most plentifully distributed by loops beneath the odonto- 

 blastic layer — the odontoblasts clothing the exterior, stand on all 

 sides perpendicular to the surface on which they are placed, and in 

 close contact with each other ; roughly speaking, they may be 

 compared to grains on the head of Indian corn — under the 

 microscope this layer of odontoblasts bears a remarkable resem- 

 blance to what is seen when we examine a section of dentine cut 

 transversely to the tubes. The microscopical character of an 

 odontoblast has been dealt with in my former paper, but, to be in- 

 telligible, I must again revert to that description. In the human 

 subject, which especially concerns us this ' evening, the odonto- 

 blast is of an oval shape, having a slender fibril at either end, and 

 its centre occupied by a well-defined nucleus. 



The internal portions of the pulp are of a fibrous character, 

 being composed of connective tissue with many fusiform nuclei dis- 

 persed throughout it ; but this structure is not concerned in the 

 formation of the dentine, that being formed exclusively by the 

 odontoblastic layer. We have, then, in an odontoblast an active 

 agent which, acting after the manner of a secreting organ, deposits 

 the salts of lime in and around itself, and, being continuous with 

 similar cells more deeply seated in the pulp, as it becomes calcified 

 and used up, the work is taken up by the deeper layer, till the at 

 first thin shell of dentine gradually thickens, and the process 

 ceases when it arrives at the stage of growth with which we are all 

 familiar. This, then, is a very brief outline of the devekmnient 

 of the second element in the hard dentine structures. 



The tooth now begins to elongate itself, and the fang to form, 

 and here another structure will present itself for our examination 

 — this is the cementum, or, as it is called in some works, " the 

 crusta petrosa." It becomes developed from the remains of the 

 dental sac, and after the manner of true bone, to which it bears a 

 resemblance in some of its characters, and to which I will refer in 

 the proper place. I trust this brief and, 1 fear, meagre outline of 



