18 REPORT — 1841. 



lal substance consists of a uniform structureless substance, and of fibres 

 passing through it." Retzius, Miiller and others leave us to conclude that 

 the interfibrous substance does not present any traces of peculiar conforma- 

 tion. Here again he was at issue with these authorities ; for he believed, 

 and hoped he could demonstrate, both by preparations and diagrams (a great 

 and interesting variety of which were exhibited to the Meeting), that the 

 interfibrous substance of the ivory was not only organized, but peculiarly 

 and characteristically organized in different animals, so as to be capable of 

 affording valuable aid to the naturalist in classifying the animal kingdom. 

 In short it was cellular : tliis he had first learnt in examining a delicate sec- 

 tion of the fossil tooth of a Rhinoceros; afterwards he had found the same 

 appearances in recent teeth ; and subsequently in all the specimens which he 

 had examined. 



3. Mr. Nasmyth had examined the fibres of different teeth, and had gene- 

 rally found that they presented an interrupted or baccated appearance, as if 

 they were made up of different compartments. The size and relative posi- 

 tions of the portions or divisions of a fibre differ in various series of animals. 

 In the human subject, each compartment is of an oval shape, and its long 

 small extremity is in apposition to the one next adjoining. The long axis of 

 the oval corresponds to the course of the fibre. In some species of the mon- 

 key tribe, the fibre appears to be composed of two rows of compartments 

 parallel to each other, and a trace of the same appearance is evident even in 

 some of the principal ramifications of the fibres. (Diagrams exhibiting the 

 peculiarities of the fibres in the human subject, the Oran-outan, the Baboon, 

 &c., were laid before the Meeting.) 



After teeth have been submitted to the action of acid, the animal residue 

 will be found to consist of fibres in which the baccated conformation just 

 described can at once be seen. Mr. Nasmyth here displayed numerous dia- 

 grams, showing the cells and fibres of the ivory in different stages of decom- 

 position by acid. The diameter of the fibres he had found to correspond 

 exactly to that of the diameter of the calibre of the tubes described by Ret- 

 zius. He had decomposed the ivory in a solution of caustic potash, but had 

 not gathei-ed any new results from this experiment, owing to the brittle na- 

 ture of the residue, the difficulty of washing it without breaking down the 

 structure, &c. ; but still the appearances displayed in this process of decom- 

 position were such as decidedly to authorize the position, tliat the ivory 

 consists exclusively of layers of cells. 



4. Mr. Nasmyth stated, that having convinced himself of the peculiar 

 cellular structure of the ivory, he had engaged, with additional interest, in 

 the examination of the pulp, the organ by which the ivory is produced. Its 

 external surface, he said, presented a remarkable number of minute ceils, in 

 a vesicular form, which are found on further inquiry to form the principal 

 portion of the bulk of the pulp. The surface, moreover, has a peculiar re- 

 ticular conformation (described in section 5.). The size of the vesicles of 

 the pulp varies from probably a diameter of tq^q o*'^ P^^'*- ^^ ^" ^"^'^ **^ H^'^ 

 of an inch. They are disposed in layers, and are of various shapes. Layers 

 of macerated pulp are found to be irregular, reticulated, and interspersed 

 with granules. Vessels in a direction which is generally vertical traverse 

 the parenchyma. Mr. Nasmyth had frequently been struck with the rapid 

 and frequent diminution in the substance of the pulp, which sometimes oc- 

 curs. There are even cases in which it would seem to be almost annihilated, 

 and this takes place more frequently in adult than in temporary, in other- 

 wise healthy than in diseased teeth. Mr. Nasmyth thought this phsenomenon 

 might be accounted for by a peculiar collapse in the congeries of cells com- 



