IMPORT OF THE NUCLEUS AND CELL-CONTENTS. 39
cell. Within the cell, for example, we see pigment, without the nucleus containing any. Within a smooth muscular fibre-cell, the contractile sub-
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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 muscular fibre-cell from the intestines, c. Portion of a nerve-fibre with a double contour, 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.
