40 



MANUAL OF PHYSIOLOGY. 



the other, and ultimately the adult nerve tissue is found to be 

 made up of nerve or ganglion cells, nerve fibres, and special nerve 

 endings. The fibres commonly act as lines of communication be- 

 tween two cells ; they connect together the numerous cells in the 

 various parts of the brain and spinal cord, or pass between the 

 cells of these central nerve organs and special cells situated through- 

 out the body, which might be called the peripheral nerve organs. 

 The simplest idea then of a special nerve apparatus is a fibre 

 connecting two cells. The peripheral cell may be a receiving organ 

 (fig. 17, s), from which, when stimulated, impulses are transmitted 



FIG. 17. 



FIG. 18. 



FIG. 17. S. Sensory receiving organ with attached afferent nerve fibre. 

 G. Central organs ganglion cells. M. Peripheral organ and efferent 

 nerve. 



FIG. 18. Three medullated nerve fibres, the medullary sheath of which 

 is stained dark with osmic acid. N. Nodes of Kanvier. Two non-medullated 

 nerve fibres, with nuclei in the primitive sheath. 



along the fibre to the central nerve cell, where they give rise to 

 certain impressions, and so we have a sensory nerve apparatus. 

 Or the central nerve cell may be the receiving agent, getting 

 stimuli from its central neighbors, and transmitting impulses to 

 a peripheral nerve terminal, by which the energy is, as it were, 

 handed over to a muscle (M) or gland, and so we have a simple 



