8oi 



nerve, and cause contraction of the diaphragm, or with the recurrent 

 laryngeal nerve, and cause movement of the vocal cords, or with 

 the spinal accessory, and cause contraction of the sterno-mastoid 

 muscle. Conversely, the phrenic nerve, when united with the cer- 

 vical sympathetic, can, when stimulated, produce the usual effects 

 observed on exciting the latter nerve (Langley and Anderson). 



Central and Autogenetic Theories of Regeneration. Although 

 the establishment of connection with the central end of the 

 cut nerve is necessary for complete regeneration, it must not 

 be supposed that no share whatever is taken in the process by 

 the peripheral stump. Even while it remains completely isolated 

 from the central nervous system, changes occur which are often 

 described as the third or final stage of degeneration, but which are 

 more correctly interpreted as forming a stage in the regenerative 

 .cycle. Spindle-shaped cells or fibres with elongated nuclei make 

 their appearance, produced by the proliferation of the nuclei of the 

 primitive sheath already described, and the increase of the proto- 

 plasm in which these nuclei are embedded. These so-called axial 

 strand fibres or this fibrillated protoplasm may appear long before 

 the remains of the degenerated axis-cylinder and myelin sheath 

 have been completely removed. It is generally acknowledged that 

 in the adult they do not develop beyond this, so long as the peri- 

 pheral portion of the nerve remains completely isolated, but neither 

 do they disappear even after a very long interval. When strict 

 precautions against union with other nerve-trunks were taken, the 

 radial nerve of an adult cat was found in this resting-stage nearly 

 a year and a half after division, and the same was true after two 

 years and a half in a nerve divided in a human being. The fibres 

 are incapable of being excited or of conducting nerve impulses. 

 The precise relation between these axial strand fibres of the peri- 

 pheral stump and the myelinated fibres found there after regenera- 

 tion has been much debated. All are agreed that nerve-fibrils 

 sprout from the central stump, and the weight of evidence is in 

 favour of the long-accepted view that it is by the growth of these 

 fibrils along the peripheral stump that the new axons are formed, 

 and that all the changes in the distal portion of the nerve, however 

 important for directing and perhaps sustaining the growth of the 

 central fibrils, are subsidiary to this. But some maintain that the 

 outgrowing central fibrils meet and unite with corresponding fibrils 

 sprouting from the peripheral stump, and that the new axis- 

 cylinders arise from the fibrils of the axial strand. It is said that 

 very shortly after being brought into connection with the central 

 portion of the same or of another nerve by careful suturing the 

 spindle cells begin to lengthen, and form non-medullated fibres, 

 like those of the sympathetic. Four weeks after union the afferent 

 fibres, although still non-medullated, are capable of being stimulated 



51 



