THE TEETH. 



51 



parent in thin sections and much more brittle and harder than 

 the other dental structures, so that it is hardly touched by the 

 knife, and yields sparks with steel (Nasmyth). Chemically, it 

 may be regarded as osseous substance, containing the smallest 

 possible proportion of organic matter ; but whether the latter 

 belong to the class of collagenous substances or not is un- 

 certain. According to Von Bibra, the enamel contains : 



Phosphate of lime, wi 



of calcium 

 Carbonate of lime 

 Phosphate of Magnesia 

 Salts . 

 Cartilage . 

 Fat . 



From a Molar of a 

 Woman 25 years of age. 

 luoride 



81-63 

 8-88 

 2-55 

 0-97 

 5-97 

 a trace 



From a Molar of 

 an adult Man. 



89-82 

 4-37 

 1-34 

 0-88 

 3-39 

 0-20 



Organic matters . 

 Inorganic matters 



10000 



5-97 

 94-03 



100-00 



359 

 96-51 



The enamel, as its fibrous structure indicates, consists 

 entirely of the so-called prisms or fibres of the enamel, (fig. 

 189) ; long, solid prisms of 0-0015 — 0-0022'" breadth, irregular 

 in shape, but commonly hexagonal or penta- Fig. 189. 



gonal, which usually occupy the whole thick- 

 ness of the enamel, resting with one extremity 

 upon the dentine, and with the other upon 

 Nasmyth's membrane. In adult teeth, these 

 elements may be very readily detected in 

 transverse and longitudinal sections, but can 

 hardly be isolated for any great length ; it is otherwise in 

 young or developing teeth, where the enamel is much softer 

 and may be cut with a knife. In such isolated prisms, whose 

 broken ends may by accident appear pointed, whence they have 

 been called " enamel needles," the surfaces and edges may be 

 very well seen. We may also very frequently observe upon 

 them, particularly after the addition of dilute hydrochloric 

 acid, more or less distinct transverse striae 0*0014 — 0-002"' 



Fig. 189. Surface of the enamel, with the ends of the enamel prisms, 

 From the Calf. 



350. 



