FUNCTIONS OF NERVE CELLS. 



513 



and have processes branching off from them, by means of which 

 they communicate with the nerve fibres. These processes may 

 be single or many, hence they are spoken of as uui-, bi-, or mul- 

 tipolar cells, etc. The nucleus is commonly very distinct, and 

 contains a well-marked nucleolus. The abundant protoplasm, 

 which is usually contained in a delicate cell wall, is in direct con- 



FIG. 205*. 



Multipolar cells from the anterior gray column of the spinal cord of the 

 dog-fish (a) lying in a texture of fibrils ; (6) prolongation from cells ; (c) 

 nerve-fibres cut across. (Cadiat.) 



nection with the axis cylinder of the nerve fibres, with which it 

 communicates by means of thin strands of protoplasm that pass 

 out from the cell by the processes. A delicate striation of the 

 protoplasm may sometimes be recognized, indicating the course 

 of the nerve fibrils as they run into the cells from the processes. 



THE FUNCTIONS OF NEKVE CELLS. 



Any mass of living protoplasm, such as an amoeba, can receive 

 extrinsic impulses, which affect directly its conditions, and though 

 the impression may be very localized in its application, yet all 

 the parts of the cell participate in the sensation, and probably 

 take part in the resulting movement. 



43 



