The MtcRoscopte. 35 



having been outlined in paper, the glass slide was lightly smeared 

 over with a fixitive of egg-albumen 2 parts, glycerine 1 part, and 

 placed over the outlined paper. Upon this slide the ribbon of 

 sections was arranged to read like the lines of a book, and gentle 

 pressure with the finger tips fixed them in place. The slide is 

 heated until the paraffin melts, then it is immersed in benzol 

 when it remains five minutes, or until the paraffin is dissolved, 

 when it is cleared in oil of cloves and mounted in balsam. 



In order properly to differentiate bone and enamel let us briefly 

 consider the development and structure of each. What is bone? 

 " Bone is simply an aggregation of calcospherules " (I quote 

 this and several of the following passages from Sudduth). The 

 calcospherules are but houses occupied by the osteoblasts, a spe- 

 ialized cell destined to perform a special work, namely that of 

 building the bony splierule which is called the calcospherule. 

 Before the osteoblast begins to perform its function as a bone- 

 builder by throwing out a thin covering, thus completely encas- 

 ing itself, it has attained its greatest size and from this time on the 

 covering or calcospherule grows at the expense of the osteoblast, 

 so that a section of newly formed bone will reveal a mass of cal- 

 cospherules united in no regular order, and the osteoblasts may 

 frequently be seen lying within, having been reduced to one-third 

 or one-fourth of their former dimensions. (See Fig. 1, o.) 



Each osteoblast secrets its calcospherule, and when this pro- 

 cess is complete, its work as a bone-builder is at an end ; from 

 this time onward it simply "occupies the house it has construct- 

 ed," ready, should occasion require, to repair any damage which 

 may be done to its individual bone. From this it might be in- 

 ferred that each osteoblast lived the life of a hermit, having no 

 communication with its surroundings. Such is not the case. 

 When the calcospherule is being formed, the osteoblasts, which 

 previously were in contact with each other, do not break up these 

 points of contact but permit them to be drawn out into fine pro- 

 cesses, and these continue to establish a union between the cells 

 of bone. 



The canals in which these processes lie have been known as 

 the canaliculi, the interior of the calcospherules themselves as 

 the lacunse, while the capillary circulation in bone comprises the 

 " Haversian canals." From these canals, through the intercom- 

 munication of the processes, the osteoblasts receive nutrient ma- 

 teriaL 



