NERVE-CELLS. 1 27 



Nucleus and protoplasm, the inner cell-kernel and the 

 outer cell-slime, are the only two essential constituents of 

 every genuijie cell. Everything else which occurs in and 

 on the cell, is of secondary importance, as it develops after- 

 wards ; the membrane, which may be variously constituted, 

 and is often very thick ; the intermediate cell-mass, or inter- 

 cellular substance, which is secreted between the contiguous 

 cells ; and also the bodies of various kinds contained in the 

 cell, such as fatty particles, crystals, grains of colouring 

 matter, water-vesicles, etc. All these are subordinate and 

 passive parts, which are formed by the activity of the 

 protoplasm or are taken up from without, and are of no 

 interest to us at present. The nucleus and the protoplasm 

 are the only two active, essential, and always present parts 

 of the cell-organism. 



In contrast to the simple cell (Fig. 1, p. 122), let us 

 compare with it a large nerve-cell, or ganglion-cell of the 

 brain. The egg-cell potentially represents the whole 

 animal — that is, it possesses the capacity to develop from 

 itself the entire multi-cellular animal body; it is the 

 common mother of all the generations of innumerable cells, 

 which form the various tissues of the animal body : in a 

 certain sense it unites in itself their various powers, but 

 only potentially, only in design. In direct contrast to this, 

 the nerve-cell of the brain (Fig. 7) is an extremely one- 

 sided formation. It cannot, like the egg-cell, develop 

 from itself numerous generations of cells, of which some 

 transform themselves into skin-cells, some into flesh-cells, 

 and others into bone-cells, etc. But instead, the nerve-ceU 

 which is formed for the highest activities of life, possesses 

 the capacity to feel, to will, to think. It is a true mind- 



