290 DENTINE. [BOOK i. 



Microscopic Qn examining very thin sections of dentine it is 



miCTo tU chem found to consist of very fine tubes the dentinal 

 cai reactions tubules, which are surrounded by a homogeneous ground 

 of dentine. substance; these tubules open internally in the pulp 

 cavity, from which they pass outwards, dividing and inter-communi- 

 cating. Sections made at right angles to their long axes exhibit the 

 tubes as minute round holes scattered through a translucent homo- 

 geneous matrix. 



When teeth are placed in the acid solutions which have been 

 recommended for decalcifying bone (see p. 2740, the mineral matters 

 which give intense hardness to the hard tissues are dissolved, and it 

 then appears that around the lumen of the dentinal tubule there is a 

 structure which may be called the dentinal sheath, which, as it resists 

 the action of acids, obviously differs from the matrix more external to 

 it; the dentinal sheath possesses apparently the characters of yellow 

 elastic tissue. Under similar circumstances, the dentinal sheath may 

 occasionally be seen to contain a fine fibre, the dentinal fibre > which 

 is a process from the pulp, probably a process from the odontoblasts of 

 the pulp. 



Relation of ^ we except the substance which constitutes the 



dentine to dentinal sheaths and which is not affected by pro- 



bone - longed boiling, nor by the action of acids or alkalies, 



dentine has a composition which very closely resembles, or rather 

 which is almost identical with, that of bone; it consists, namely, of a 

 collagenous organic basis in which are deposited mineral matters 

 identical with those of bone. 



The collagenous organic basis impregnated with salts is the result 

 of the activity of those connective-tissue cells which we term odonto- 

 blasts, just as the matrix of bone proper was originally formed through 

 the activity of those connective-tissue cells which we designated 

 osteoblasts. Though differing somewhat in arrangement and in texture, 

 the two tissues, dentine and bone, are, on developmental as well as on 

 chemical grounds, seen to be identical. 



As Hoppe-Seyler has well shewn, the dentinal sheaths correspond to 

 the more internal portion of the ground substance of bone which may be 

 separated as a distinct investment bordering the lacunae, canaliculi and 

 Haversian canals (see p. 273). 



water and Fresh dentine, when dried, loses about 10 per cent, 



organic mat- of water ; the quantity of organic matter contained in 

 ter of dentine, ft varies between 26 and 28 per cent., on an average 

 being about 28 per cent. 



constitu- Although a large number of analyses of tooth have 



tion of the been made, we possess fewer absolutely reliable analyses 

 mineral mat- of dentine than of enamel. Dentine, like bone, cen- 

 ters of den- tains, as its chief mineral ingredients, calcium and 

 phosphoric acid ; the proportion of carbonic acid found 

 in its ash by most analysts is smaller than in bone. Hoppe-Seyler 



