IMPORT OF THE NUCLEUS AND CELL-CONTENTS. 



39 



FIG. 



cell. Within the cell, for example, we see pigment, 

 without the nucleus containing any. Within a smooth 

 muscular fibre-cell, the contractile sub- 

 stance is deposited, which appears to be 

 the seat of the contractile force of mus- 

 cle ; the nucleus, however, remains a 

 nucleus. The cell may develop itself into 

 a nerve-fibre, but the nucleus remains, 

 lying on the outside of the medullary 

 [white 1 ] substance, a constant constituent. 

 Hence it follows, that the special peculiar- 

 ities which individual cells exhibit in 

 particular places, under particular circum- 

 stances, are in general dependent upon the 

 varying properties of the cell-contents, 

 and that it is not the constituents which 

 we have hitherto considered (membrane 

 and nucleus), but the contents (or else the masses 

 of matter deposited without the cell, intercellular), 

 which give rise to the functional (physiological) dif- 

 ferences of tissues. For us it is essential to know 

 that in the most various tissues these constituents, 

 which, in some measure, represent the cell in its abstract 

 form, the nucleus and membrane, recur with great con- 

 stancy, and that by their combination a simple element 

 is obtained, which, throughout the whole series of living 

 vegetable and animal forms, however different they may 

 be externally, however much their internal composition 

 may be subjected to change, presents us with a structure 



Fig. 5. a. Pigment-cell from the choroid membrane of the eye. b. Smooth mus- 

 cular fibre-cell from the intestines, c. Portion of a nerve-fibre with a double con- 

 tour, axis-cylinder, medullary sheath and parietal, nucleolated nucleus. 



1 All words included in square brackets have been inserted by the Translator, and 

 are intended to be explanatory. 



