82 W. H. F. ADDISON AND J. L. APPLETON, JR. 
seen in the fully developed teeth. The osteodentine of the 
tip of the tooth is softer than is true dentine, for when the young 
tooth is dried this end shrivels and darkens in color. This cap of 
osteodentine on the end of the tooth may be useful, as suggested 
by Sachse (’94), because of its softness, in allowing the early 
formation of the functional occlusal surface. When this soft 
substance begins to wear away the tissues of the pulp would 
soon become exposed were there not a provision for the filling 
in of the apex of the pulp-chamber. This is effected by the 
formation of an irregular hard matrix, which may also be called 
osteodentine, within the extremity of the pulp-chamber. As 
Fig. 24 Isolated upper and lower incisors of several ages of young albino 
rats. The pointed shape just before eruption is seen at 7 days. At 12 days, 
there is yet very slight change in the apices. At 21 days the occlusal surfaces 
are concave, and at 26 days they have nearly the typical mature appearance. 
x 2. 
the outer surface of the tooth wears away, this formation is 
constantly taking place a short distance from the occlusal 
surface. 
Thus in examining a longitudinal section of the tooth at an 
age when the process of attrition has begun, and the typical 
occlusal surface has been formed (e.g., 26 days, fig. 23), we find 
this form of secondary dentine or osteodentine filling in the 
distal extremity of the pulp-chamber. As one approaches the 
anterior end of the pulp-chamber, the pulp becomes more and 
more restricted and the blood-vessels appear congested. Pro- 
ceeding distally, the irregular matrix formation is seen between 
the cells and blood-vessels and finally near the occlusal worn 
surface is a granular mass of osteodentine with no circulating 
blood in it, but spaces are still seen containing the remains of 
the pulp elements. Here the living elements have disappeared, 
