612 MANUAL OF PHYSIOLOGY. 



channels for the transmission of nerve impulses from one cell or 

 terminal to another. 



The nerve or ganglion cells are remarkable for their large size, 

 their large, clear nucleus, distinct nucleolus, and fibrillated pro- 

 toplasm. They have, at least, one more commonly several 

 processes connected with them, and are commonly called uni-, 

 bi-, or multi-polar cells. Often one of these processes is more 

 distinct and more definite than the others, and does not subdivide 

 into branches like them. It appears to be connected directly 

 with the axis cylinder of a medullated nerve fibre. 



FIG. 238. 



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.) 



The nerve cells can conduct the nerve impulses which reach 

 them by any of their attached poles, and they can transmit these 

 impulses on to other cells by means of their protoplasmic strands 

 of intercommunication. They thus frequently seem to direct an 

 impulse coming by a sensory or afferent nerve from the surface 

 back again by an efferent nerve to some texture or organ in the 

 neighborhood. Thus, the slightest stimulation of the conjunctiva 

 causes immediate and involuntary winking of the eyelid. This 



