STRUCTURE OF THE ENAMEL. 473 



Kolliker; but I must still consider it doubtful whether all enamel 

 prisms exhibit transverse striae and varicosities. Hertz returns to the 

 intermittent (schubweise) calcification of the enamel cells formerly 

 admitted by Hannover (39). But the mode in which so regular a 

 transverse striation is thus produced, is, to me at least, unintelligible ; 

 besides, no evidence can be brought forward showing that a laminated 

 mode of formation occurs in enamel. 



The enamel fibres lie in close contact with each other, with- 

 out any demonstrable intervening substance. They appear to 

 be completely solid, and extend for the most part through the 

 whole thickness of the enamel. At the same time they pursue 

 a very various course, which finds its expression in the well- 

 known decussation of the prisms. We accordingly find that 

 alternate layers of enamel fibres appear on section to run verti- 

 cally and transversely, in consequence of which a peculiar and 

 sometimes very regular pattern is produced. The enamel prisms 

 must therefore also pursue, in the form of fasciculi, a various and 

 often decussating course towards the surface of the tooth. A 

 second pattern presenting itself in the enamel is formed by the 

 so-called brown parallel strice of Retzius, which are superim- 

 posed lines coursing in the same direction, and regarded by 

 Kolliker as the expression of a laminated mode of formation of 

 the enamel. 



These are frequently (see fig. 97) very fine, and closely applied to 

 one another; some appearing to be more conspicuous than others. 

 No satisfactory explanation of this phenomenon can at present be 

 given. Hertz attributes it to deposits of pigment in the enamel prisms, 

 as occurs, for example, in the beaver and squirrel, where it is due, 

 according to V. Bibra (68), to the presence of oxide of iron; and in 

 these Rodents, according to Wenzel (66), such deposits are already 

 present in the protoplasm of the enamel cells ; still, no positive state- 

 ments can at present be made on this point. Other kinds of strias, again, 

 may be perceived on examining transverse sections, and most distinctly 

 after brushing with dilute hydrochloric acid (1 : 12, Hertz), which 

 are caused, according to Czermak, by the regular zigzag course, or, 

 according to Hannover, by twisting or spiral turns of the prisms. An 

 explanation will be hereafter given of the decussation of the prisms, 

 as well as of their various course (see the Development of the Enamel). 

 The observations of Hoppe-Seyler (69) on the behaviour of the enamel 



