ELEHENTABY STBUCTUKE OF OBGANIZED BODIES. ly 



the fibrils, or upon the inner aspect of the cell-.membrane of 

 the secondary nervous cell. This secondary deposit is a 

 fatty white-coloured substance, and it is through this that 

 the nerve acquires its opacity (fig. 7, b). Superiorly, the fibril 

 is still pale ; inferiorly, the deposition of the white substance 

 has occurred, and its effect, in rendering the fibril dark, is ob- 

 vious. With the advance of the secondary deposit, the fibrils 

 become so thick, that the double outline of their parietes comes 

 into view, and they acquire a tubular appearance (fig. 7, c). 

 On the occurrence of this secondary deposit, the nuclei of the 

 cells are generally absorbed ; yet a few may still be found to 

 remain for some time longer, when they are observed lying 

 outwardly between the deposited substance and the cell-mem- 

 brane (fig. 7 c), as in the muscles. The remaining cavity of 

 the secondary nervous cell appears to be filled with a pretty 

 consistent substance, the band of Remak, and discovered by 

 him. In the adult a nerve consequently consists, 1st, of an 

 outer pale thin cell-membrane the membrane of the original 

 constituent cells, which becomes visible, when the white sub- 

 stance is destroyed by degrees (ex. yr. fig* 7, d) ; 2nd, of a 

 white fatty substance, deposited on the inner aspect of the 

 cell-membrane, and of greater or less thickness ; 3rd, of a 

 substance which is frequently firm or consistent, included 

 within the cells, the band of Remak.* 

 [56. From this resume, it would 



appear that the universal elementary 



form of every tissue is the CELL, which / 



is preceded by the NUCLEUS as medi- **" 



ate, and the JSTUCLEOLUS as immediate 



products of the formative power. Cells 



and nuclei seem to stand in mutual and 



relative opposition; so that generally, Fig- 8. Cells from the 

 i 11 Vi i -i I granulations of the umbi- 



perhaps invariably, the one is evolved at f ical cord of the calf Th 



the expense of the other (fig. 8). After bear a striking resem- 

 these transition stages are accom- blance to the cellular tis- 

 plished, the tissue attains individuality sue of vegetables ; nuclei 



according to the general character and are se f lf lud t e f in the 



i ,-, -T. several cells. After Bres- 



place it occupies m the system. Dur- chet and G1 (Ann des 



uig this last stage the more distant Sc.Nat.t.\iu.-pl. 6,fig.5). 

 * Dr. Schwann, in Professor Wagner's Physiology, p. 222. 



c2 



