DR. BEALE, OX THE TISSUES. 15 



transude through the walls of the vessels, and are supposed 

 to pass along the tubes to the outer part of the tooth. More- 

 over, in some cases certain of the so-called dentinal tubes are 

 completely solid, the tube being obliterated. 



The specimens which have been sent round prove, the lec- 

 turer thinks, that the formation of the dentine and the so- 

 called tubes, is effected in a much more simple manner than 

 is usually believed. The elongated masses of germinal matter 

 first of all -produce foi-med material, which gradually increases 

 as in other cases, upon the outer surface of the germinal 

 matter. The formed material of the adjacent elementary 

 parts is continuous, and calcareous matter is first deposited 

 in the oldest part of this formed material. The calcareous 

 matter appears in the form of small globules, which gradually 

 increase in size, and often several coalesce. Thus the formed 

 material, or matrix, of the dentine becomes calcified. 



Not unfrequently, hoAvever, several of the calcareous glo- 

 bules increase in such a way as to enclose a portion of un- 

 calcified matrix. This being, as it were, imprisoned by hard 

 impermeable structure retains its soft primitive state. If the 

 tooth be dried the soft matrix in these spaces shrinks and 

 air rushes in. Thus the appearance known as '' globular 

 dentine " is produced, and the reason why uncalcified tubes 

 are seen traversing these spaces becomes manifest. 



After the matrix of the dentine is calcified the germinal 

 matter still slowly undergoes conversion into formed material, 

 which in its turn becomes impregnated with calcareous 

 matter. The germinal matter diminishes in thickness. The 

 formed material is produced more slowly after the general 

 basis has been laid down, and hence the dentine immediately 

 surrounding the tube seems to be distinct from that lying in 

 the intervals between the tubes. The germinal matter gra- 

 dually shrinks from the outer part of the dentine (the oldest 

 portion) towards the x^ulp-cavity, where these changes still 

 go on. In the dry tooth the same fact may be expressed by 

 saying that the narrowest part of the dental tubes is at the 

 circumference of the dentine, and this part was the first 

 formed ; the widest part is that which is in contact with the 

 pulp, and this is composed of dentine most recently developed. 

 Internal to this is a narrow layer, tlie formed material of 

 which is still soft and not yet calcified. 



The appearances described can only be demonstrated in 

 perfectly fresh teeth, which have been placed in carmine 

 solution very soon after extraction. 



The principal changes in such a tissue as dentine seem to 

 consist of the conversion of germinal matter into formed 



