636 NERVE-DEGENERATION AND NERVE-REGENERATION. 



a degree as to convert the entire peripheral portion of the nerve into a connective- 

 tissue strand, the fragments formed at the same time undergoing absorption. In 

 the motor end-plates degeneration likewise takes place, at first in the non-medul- 

 lated fibers, then in the terminal filaments and lastly in the nerve-trunk. 



If regeneration takes place, the extremities of the divided nerve must 

 have united, and for this purpose in the human being nerve-suture has 

 been employed. 



In the middle of the fourth week small, bright bands, developed from the 

 proliferated protoplasm, appear within the sheath of Schwann, and these penetrate 

 between the nuclei and the remains of the myelin (E). They are the new axis- 

 cylinders, which thus develop in an endogenous manner within the old sheath of 

 Schwann. Soon they become thicker, and receive myelin, with Lantermann's 

 clefts, Ranvier's nodes and sheaths of Schwann (from the 26. to the 3d month) 

 (F). According to Ziegler the new axis-cylinder, which develops independently, 

 becomes only later connected with the central stump. The formation of the 

 myelin takes place continuously. A portion of the nuclei disappear; the outer, 

 with their protoplasmic portion, give rise to the sheaths of Schwann. Exactly the 

 same process takes place in nerves ligated in continuity. It is a remarkable fact 

 that several new fibers may develop within an old fiber. From the central ex- 

 tremity of the divided nerve-fiber the axis-cylinder after the fourteenth day grows 

 toward that of the newly formed fiber and unites with it. The central extremity 

 of a divided motor nerve may unite with the peripheral extremity of another 

 nerve and still functionate. Langley united the central extremity of the vagus 

 with the peripheral extremity of the sympathetic, and found after union took 

 place that the vagus had acquired control of all structures supplied by the cervical 

 sympathetic. According to Gessler restoration of the end-plate occurs first in 

 the process of regeneration; In the case of non-medullated fibers the contents 

 only and not the sheaths degenerate from the third day on. After two days 

 perceptible regeneration begins. 



The regeneration of nerves is under the influence of the nerve-centers 

 acting as nutritive centers. If nerves be completely and permanently 

 separated from these centers regeneration will not take place. 



In the regeneration of mixed nerves sensation returns first, then vol- 

 untary muscular movement, and finally movement on irritation of the 

 motor branches. 



As the fatty degeneration involves the peripheral extremity of the nerve the 

 observation of this process in a divided nerve affords a means of determining 

 the central origin of fibers in a complex arrangement of nerves. The division of 

 motor nerves results also in fatty degeneration of the related muscles in case 

 restitution does not take place. 



After division of the axis-cylinder the nerve-cell from which it origi- 

 nates undergoes alteration, the Nissl bodies swelling and disintegrating, 

 though later being restored. In the process of degeneration the cell in- 

 creases in volume and the nucleus assumes a peripheral position. This 

 period covers from one and three-fourths to twenty days. Restitution 

 occupies about ninety-two days. These changes are indications not of 

 paralysis of the cells, but only of a certain impairment of their func- 

 tion. If the degeneration is permanent the cell disintegrates. 



Under the influence of various procedures, such as crushing of the 

 nerve-fiber, the remarkable observation has been made that voluntary 

 impulses or irritating influences originating above the site of compression 

 are conducted through the nerve to the muscle and give rise to con- 

 traction, while the irritability to stimuli below the site of compression 

 is greatly diminished. Nevertheless Erb did not observe this difference 

 with respect to mechanical stimulation. In an analogous way it will 



