20 REPORT — 184L 



the pre-existing cells of the pulp. (Here diagrams of different layers of cells 

 in various stages of ossific transition were exhibited to the Meeting.) The 

 fibres of the tooth, as it appeared to Mr. Nasrayth, are derived from the frame- 

 work of the reticulations : at any rate, the fibres bounding the reticulations 

 are precisely analogous in diameter and direction to the subsequent fibres of 

 the tooth. He exhibited diagrams also in confirmation of this view*. 



6. The laminated cellularity of the ivory, M'hich Mr. Nasmyth had shown 

 was a natural consequence of the cellular structure of the pulp, was also borne 

 out, he thought, by facts coming under daily observation, or recorded by sci- 

 entific inquirers, which could not be explained by any other theory ; viz. by 

 the evidently laminated and concentric structure of the teeth of the mammoth, 

 which is rendered directly evident during their decomposition ; by the expe- 

 riments of Hunter on the teeth of animals fed on madder ; by the circumstance 

 that ivory is found to possess considerable strength if cut parallel to the long 

 axis of the tooth, and that it is weak if cut at right angles ; and also by many 

 other phasnomena of frequent occurrence. 



7. When the growth of the ivory is completed, the primary function of the 

 pulp ceases ; but its residue, under the influence of disease, is often observed 

 to ossify in different parts of its substance. The bony substance thus formed 

 resembles, when viewed under the microscope, the irregular ivory constituting 

 the teeth of many of the lower animals, of fishes for instance, in which the 

 pulp becomes entirely ossified. It consists of irregularly radiating filaments, 

 blended with small calcigerous cells, in which ossified vessels ai'e seen to ra- 

 mify. In some animals, such as the Bradypus, Trichecus Rosmarus, Mega- 

 therium, &c., the pulp ceases at a certain period to be converted into ivory, 

 and a peculiar and imperfect bony substance is then formed, until the whole 

 of the pulp becomes ossified. In short, the simplest forms of teeth are almost 

 exclusively composed of this substance ; and in many of those, which consist 

 of cement and ivory without enamel, it fills up the internal cavity. It is so 

 frequently present, is so perfectly different from the other dental formations 

 in the mode of its development, the nature of its function, and the appear- 

 ance which it presents, that in Mr. Nasmyth's opinion it merited the appella- 

 tion of the fourth distiiict constituent substance of the tooth. It is of frequent 

 occurrence in the human subject, but anoi'mally, and in every case in which 

 he had met with it, as the sequela of long-continued disease, either of the tooth 

 itself or of some part of the mouth ; but still he said it was proper to observe, 

 that there is no direct evidence to prove that ossification of the residue of the 

 pulp may not take place in the human subject without previous morbid sym- 

 ptoms. 



8. The results of Mr. Nasmyth's investigations into the structure of the 

 enamel were not quite in accordance with those of recent writers on the sub- 

 ject. Retzius, Purkinje and othei-s had stated that the enamel consists of 

 fibres running in a direction from the centre to the circumference of the 

 tooth. On making a section of the enamel parallel to the transverse diame- 



* Before quitting this part of the subject, Mr. Nasmyth alluded to the recent researches of 

 Schwann on the structure of elementary tissues, and with respect to the connexion which 

 that author appears only to presume to exist between the unossified pulp and the ivory al- 

 ready formed, quoted the following passage from page 125 of that author's work : " Against 

 the theory that the dental substance is the ossified portion of the pulp, the facility with which 

 the one is separated from the other has been adduced ; and I allow the force of this ob- 

 jection. Nevertheless, it is at any rate weakened by the circumstance, that a portion of the 

 pulp actually remains attached to the dental substance, and by the fact, that in half-ossified 

 ribs, for instance, the cartilage can be easily separated from the ossified portion ; and it must 

 be remembered, that in the tooth the separation must be easy in proportion to the difference 

 between the consistence of the pulp and of the dental bone." 



