356 



THE NERVOUS SYSTEM. 



FIG. 91. 



is much less rapid. When small nervous branches supplying the skin 

 have been cut, the loss of tactile sensibility in the immediate neighbor- 

 hood often persists for weeks or months after the healing of the wound. 

 Restoration may sometimes take place in larger nerves, as in a case 

 reported by L'Etievant,* where the median nerve, in a man twenty-six 

 years of age, was divided at the upper third of the arm. The power of 

 motion and sensibility, in the parts supplied by this nerve, remained 

 abolished for ten months, but began to reappear in fourteen months, 

 and were nearly restored at the end of a year and a half. But accord- 

 ing to both L'Etievant and Mitchell, f when the injured nerves in man 

 are of considerable size, the restoration of function, as a general rule, 

 is either very imperfect or does not take place at all. 



Nerve Cells. 



The nerve cells, the characteristic anatomical element of the gray 

 ; substance, are irregularly rounded bodies, consisting of a soft, nearly 

 transparent, finely granular, albuminous matter, with a large, distinctly 

 marked nucleus and nucleolus. They often contain in addition yellow- 

 ish-brown pigment grains, imbedded in the substance of the cell. They 



vary in size in different regions. The 

 smaller cells, from 10 to 20 mmm. in 

 diameter, are found in the ganglia of 

 the sympathetic system, parts of the 

 cerebral hemispheres, and the posterior 

 horns of gray matter in the spinal cord. 

 The larger, from 40 to 60 mmm., are in 

 the cerebellum and the medulla oblon- 

 gata ; and the largest of all are in the 

 anterior horns of gray matter of the 

 spinal cord, where they sometimes reach 

 the diameter of 130 or 135 mmm., or 

 seventeen times the size of the red 

 globules of the blood. 



The nerve cells are especially distin- 

 guished by their processes. These are 

 narrow offshoots from the body of the 

 cell, consisting apparently of the same 

 finely granular albuminous material. 

 Their number varies in different parts. In the Gasserian ganglion and 

 the spinal ganglia of man, as well as in those of the dog, cat, rabbit, 

 and frog, the nerve cells have each only a single process. In the 

 sympathetic ganglia in man they have several ; and in the gray sub- 

 stance of the brain, medulla oblongata, and spinal cord each cell presents 

 from three or four to seven or eight processes, running in various 



NERVE CELLS, from the anterior horn of 

 gray substance of the spinal cord. 



* Traite des Sections Nerveuses. Paris, 1873, p. 54. 



f Injuries of Nerves, and their Consequences. Philadelphia, 1874, p. 84. 



