80 FORMATION OF ENAMEL. 



curved lines, one within the other. The slight inter- 

 val between these lines corresponds to the line of 

 junction of the enamel and dentine in the fully formed 

 tooth. From this neutral line the masses of bioplasm 

 of the two rows move in opposite directions. In 

 the outer one each mass diverges outwards from the 

 neutral line while the different masses of bioplasm of 

 the inner row converge slightly as they move in- 

 wards and form dentine in their wake. 



12O. Formation of Enamel. The formation of the 

 enamel may be very successfully studied in the canine 

 tooth of a young pig. In one of my preparations, ob- 

 tained from an injected specimen, the capillaries of 

 the enamel membrane are seen to be well injected with 

 transparent blue injection, and the enamel cells, the 

 bioplasm of every one having been well stained with 

 carmine, are distinctly shown. Each appears as a 

 columnar or cylindrical body, not unlike a cell of 

 columnar epithelium, with an oval mass of bioplasm 

 nearest to its distal extremity. As the bioplasm 

 moves outwards from the neutral line above referred 

 to, it forms the column of soft material which is to 

 become the enamel rod. After some extent of soft 

 tissue has thus resulted, calcareous matter is depo- 

 sited in that part of the column which was first 

 formed. In my specimen several columns can be 

 discerned in which the change has already com- 

 menced. The highly refracting earthy particles con- 

 trast remarkably with the smooth, faintly granular, 

 organic matrix. The deposition of these earthy salts 

 may be due merely to chemical change consequent 

 upon the formation of free alkali in this the oldest 

 part of the organic matter. While this process is 

 going on, the bioplasm in each little column is still 

 moving outwards, and forming more organic matter, 

 which, in its turn, becomes calcined. This process 

 continues until the formation of the enamel is com- 

 plete, when the vessels of the membrane waste. A 



