334 MICROSCOPIC ANATOMY OF THE TEETH 



membrane was the ' membrana preformativa ' between the 

 enamel organ and the forming enamel, and Lent (4) in 

 1853 was of the same opinion. Nasmyth was the first to 

 show that a membrane could be raised from the surface 

 of formed enamel which had not been exposed to wear. 



Kolliker held that the membrane was a final product of 

 the enamel cells, while Waldeyer considered it was derived 

 from the external epithelium of the enamel organ. The true 

 histology of the membrane had, however, never been demon- 

 strated until Dr. Paul published his researches (6). He sepa- 

 rated the membrane from the tooth by immersing it in acids, 

 employing in his first experiments 5 per cent, nitric acid, 

 and stripped it from the enamel, staining with silver nitrate 

 or with eosin, but later found he obtained better results by 

 decalcifying in phloroglucin and staining in Ehrlich's 

 hsematoxylin. 



These preparations demonstrated that Nasmyth's mem- 

 brane consists of two distinct layers an inner clear layer in 

 immediate contact with the enamel, and lying upon this 

 a layer or layers of epithelial cells which from their position 

 must have been derived from the enamel organ. 



In former observations on this membrane it had been 

 considered that the polygonal markings observed upon the 

 clear layer of the membrane were the impressions of the 

 enamel prisms, but Dr. Paul points out that these markings 

 are very many times larger than those caused by the enamel 

 prisms, which can also be seen in the clear layer. 



It can be seen, as shown in fig. 222, that the epithelial 

 cells are distinctly visible upon the upper surface of the 

 membrane, while the impressions of the enamel prisms from 

 beneath are also visible, and are seen in this figure in the 

 same field of the microscope as the cells and their impres- 

 sions. It needs no measurement to show the great dis- 

 proportion of size between the two sets of markings. The 

 preparations from which these photographs were taken were 

 made by the author from specimens prepared by a slightly 

 different method from that employed by Dr. Paul. The 

 membrane was floated off from the tooth in formic acid, 

 the detached fragments being well washed and stained with 

 Weigert's iron hsematoxylin. 



