THE NUTRITION OF NHRVOUS TISSUE 



847 



wound and proceed peripherally, although in the dog, in which the degen- 

 eration is rapid, it appears as though the process occurred synchro- 

 nously in all parts of the fiber. 



In the fibers on the central side of the wound degeneration also oc- 

 curs, but it is limited to the several internodal segments which lie just 

 above the point of injury. Nearer to the nerve cell body the fibers re- 

 main for the most part unchanged. An influence, howeyer, is exerted 



- 



I 



H 

 II 



i 



II 



i| 



*\\ 



IV 



VI 



Fig. 211. Degeneration and regeneration of a sectioned nerve fiber. I. Fibrillation of the axis- 

 cylinder and swelling of the myelin. II. Segmentation of the axis-cylinder, swelling and displace- 

 ment of the myelin. Proliferation of neurilemma cells. III. Disappearance of the axis-cylinder; 

 myelin bulbs; proliferated connective tissue cells. Retrograde degeneration. IV. Formation of 

 granular bodies; elimination of degenerated myelin by phagocytes. Soldering of fragments by 

 proliferated connectve tissue cells. Retrograde degeneration. V. Beginning of regeneration in the 

 central end. VI. Progression of the regenerated axis-cylinder in the empty sheath of the peripheral 

 end. VII. Regeneration of the peripheral segment. Commencement of myelin reconstruction. 

 (After Tinel.) 



on the cell body by the peripheral injury. The chromatic substance of 

 Nissl's granules becomes modified so that they lose their staining power 

 (chromatolysis), the cell becomes swollen, and the nucleus may assume 

 an eccentric position. Peripheral to the wound the destruction of the 

 tissue is complete, a fiber separated from its cell body being unable to 

 continue to live. The changes which occur on the central side of the 

 injury are usually of a temporary nature, and are restored by the process 



