NASMYTH'S MEMBRANE 337 



that these imbrication lines are constantly present in the 

 enamel of healthy teeth, and he drew attention to the fact 

 that specimens of Nasmyth's membrane stained with silver 

 nitrate show a distinct striation which he considered corre- 

 sponds to the furrows between each imbrication line. 



In fig. 224 the impressions of the individual prisms are 

 clearly visible along these lines, which evidently in this case 

 represent the summits of the ridges. 



The Cellular Layers. In some parts of the floated pre- 

 parations a single layer only of epithelial cells is seen, but 



Fro. 224. Floated preparation of Nasmyth's membrane showing 

 impressions of enamel prisms in parallel lines. ( x 250.) 



in most places there are two or many layers. The cells vary 

 considerably in size, so much so that an average measure- 

 ment will not give any clear idea of their dimensions. They 

 are mostly polygonal in outline, separated from one another 

 by a distinct interval, as in epithelia elsewhere, and these 

 channels are crossed by bridges or processes. These processes 

 are in many cases very strongly marked, and in some parts, 

 at the margins, quite thick horny projections from the cell 

 are seen. According to several authors, this strongly 

 marked fibrillation of the cell is intimately associated with 

 the condition of keratinization (Schafer). 



The cytoplasm of the cell body is clearly defined, and the 



