STRUCTURE OF NERVE-CELLS. 129 



Pio. 7. — A large branched nerve-cell, or " mind-cell," from the brain of 



an Electric Fish (Torpedo) ; 600 times the natural size. The large, bright, 

 globular kernel (nucleus) lies in the centre of the cell ; this nucleus contains 

 a nucleolus, and in that, again, there is a nucleolinus. The protoplasm of 

 the cell has separated into innumerable fine threads (or fibrillse), which are 

 embedded in the inter-cellular substance, and which pass out into the 

 branched processes of the cell. An un branched process (a) passes over 

 into a nerve vessel. (After Max Schultze.) 



cell, an elementary organ of mental activity. Correspond- 

 ingly, it has an extremely complex minute structure. Innu- 

 merable filaments of exceeding fineness, which may be com- 

 pared to the numerous electric wires of a great central 

 telegraph station, traverse, crossing each other again and 

 again, the finely granulated protoplasm of the nerve-cell 

 and pass into branched processes, which proceed from this 

 mind-cell, and connect it with other nerve-cells and nerve- 

 fibres (a, b). It is scarcely possible to trace, even approxi- 

 mately, the tangled paths of these filaments in the fine 

 substance of the protoplasmic body. 



We thus have before us a highly complex apparatus, 

 the more minute structure of which we have hardly begun 

 to know, even with the help of our strongest microscope, 

 and the significance of which we rather guess than know. 

 Its complex mechanism is capable of the most intricate 

 psychical functions. But even this elementary organ of 

 mental activity, of which there are thousands in our brain, 

 is only a single cell. Our whole intellectual life is but the 

 sum of the results of the activity of all such nerve-cells or 

 mind-cells. In the centre of each cell lies a laro;e trans- 

 parent ball, which encloses a smaller dark body. This is 

 the nucleus which contains the nucleolus. Here, as every- 

 where, the nucleus determines the individuality of the 

 cell, and shows that the entire formation, notwithstanding 



