NASMYTH'S MEMBRANE 349 



many causes, such as the elongation of the roots, the growth 

 of the bone of the jaw, the development of the periodontal 

 membrane, and the blood pressure in the vascular tissues 

 around and beneath it. 



This advancement of the tooth is therefore probably due 

 to several concomitant forces, and is one factor in eruption, 

 the other being the absorption and opening out of the 

 tissues overlying the tooth. 



Warwick James, in a previous paper (15), showed very 

 clearly how such a path is prepared by the opening out of 

 the overlying tissues of the capsule as the tooth erupts. 

 He showed that the globes epidermiques or epithelial coils, 

 as he prefers to call them, which are due to degenerative 

 changes in the epithelial elements of the capsule, form very 

 wide spaces within the connective tissue over the tooth ; that 

 these increase in size until they appear as mere openings 

 in the connective tissue, all trace of their epithelial structure 

 being lost, and they eventually open out upon the surface ; 

 but this opening out takes place not by the advance of these 

 bodies, but by a separation or rarefaction of the tissue of the 

 capsule, which is gradually withdrawn on either side of the 

 erupting crown, yielding in the first place at the situation 

 of the epithelial coils. 



The changes which take place in the epithelium of the 

 follicle and the formation of the epithelial coils have been 

 more fully considered in treating of the follicle (p. 311). 



Guido Fischer (14), in his paper on the eruption of the teeth, 

 described the union of the outer and inner layers of the 

 enamel organs into one continuous epithelial layer which 

 just previous to eruption becomes blended with the epithe- 

 lium of the mouth. These observations were made on the 

 erupting teeth of the cat, and the illustrations to the paper 

 show this epithelial layer blended with the surface epithelium 

 on either side of the opening through which the erupting 

 tooth is advancing. 



It is difficult to reconcile this description with what is 

 seen in the sections of the human follicle just before eruption, 

 described in Chapter VIII, for Fischer's figures do not show 

 the detachment of any layer or layers of cells to form 

 Nasmyth's membrane, and one would be more inclined to 



