216 TOMES, ON THE DEVELOPMENT OF THE ENAMEL. 



detached, and many float off in the fluid when the part is 

 under manipulation. If examined in this condition, some are 

 found in parallel bundles, and apparently attached slightly to 

 each other ; but many are quite unconnected (fig. 2). But 

 whether associated or single, each column will be found to 

 have a delicate small process projecting from that extremity 

 which was connected with the enamel, a process which would 

 pass through a membrana preformativa could such be shown 

 to exist. Immediately above the point from which the pro- 

 cess starts, the column has, when separated from its fellows, a 

 slight circumferential dilatation, as though the cylinder had 

 been everted at the edge when the separation was effected. A 

 close examination of the columns will, I think, lead to the 

 belief that each is composed of a delicate sheath, in which is 

 enclosed one or more nuclei, the interspaces being occupied 

 by transparent granular matter. The nuclei are usually 

 more distinct near the peripheral end of the columns ; 

 the attached extremity being commonly more granular than 

 nucleated ; but I have seen cases in which the sheath seemed 

 pretty fully occupied by nuclei. After the preparation had 

 been kept for a few weeks, the nuclei became more faint, and 

 the granular matter more apparent. 



Now, supposing the decalcified enamel fibres are detached 

 from the columns and are viewed singly, it will be seen that 

 the end which approached the dentine is clear and transparent, 

 while that which meets the columns is coarse and granular, 

 appearing by transmitted light of a deep-brown colour ; in- 

 deed, but for the colour, it would be difficult to distinguish 

 the distal extremity of the decalcified enamel fibre from the 

 proximal end of the column of the enamel organ, fig. 3. 



In many parts of the specimen the columns have been 

 wholly detached, leaving a surface similar to that figured by 

 Mr. Huxley, and described as the membrana preformativa. 

 But if we look directly at the edge of the specimen where it 

 is turned towards the observer, it will be seen that the enamel 

 fibres pass through to the surface of this apparent membrane, 

 fig. 4, a. 



The enamel fibre, in its decalcified state, consists of a fine 

 transparent and structureless sheath in the part which is fully 

 formed, but in the distal portions, where development is pro- 

 gressing, the sheath appears to contain in many instances 

 granular matter, fig. 3. 



M. Lent mentions that he had at first some difficulty in 

 obtaining the membrana preformativa, freed from enamel 

 fibres. He at length succeeded, by treating the decalcified 

 specimens with caustic potash or soda. No doubt the ex- 



