DEGENERATION AND REGENERATION OF NERVES. 355 



from the nerve-fibres the cells of the connective tissue in the neighbourhood of the 

 fibres become charged with fatty granules, which may have become formed from 

 the dissolved fatty substances of the medullary sheath. 



These degenerative changes seem to occur simultaneously along the whole 

 length of the nerve. In the nerves to voluntary muscles the end-plate is said to be 

 the part first affected. 



In the immediate neighbourhood of the section the appearances are somewhat 

 modified by the escape of the myelin from the cut ends of the nerve-fibre, and the 

 infiltration of blood and lymph into the interior of the ends thus emptied of their 

 contents. This change must of course occur both in the central stump of the nerve 

 as well as in the peripheral cut end : it does not often extend beyond the first node. 

 Apart from such traumatic modification, true degenerative changes do not occur in 

 the end of the nerve Avhich is still in connection with the centre, although prolifera- 

 tion of the nucleus in the first and second internodes near the cut may take place. 

 The central cut end of the axis-cylinder does not become altered ; except that it 

 undergoes a slight swelling, preparatory in all probability to the renewed growth 

 by which the regeneration of the fibre is effected. 



Regeneration proceeds but slowly. Up to the twenty-eighth day after the 

 section, or even later than this, there is still no trace of the new nerve-fibres in the 

 peripheral part of the nerve. With the exception of a few fibres which for some 

 reason not well understood (probably because they are derived from some other 

 nerve which has not been cut, and are taking a recurrent course in the cut 

 nerve), have not undergone degeneration, nothing is to be seen in a section 

 of the nerve at this period, except the primitive sheaths of the old fibres, filled 

 with clear or finely granular substance. If, however, a transverse section be 

 made of a nerve considerably later than this (sixty or seventy days after the 

 original section) it is found that within the tubes formed by the old primitive 

 sheaths, according to Vanlair between them, small single fibres or groups of 

 fibres, either pale or provided with a medullary sheath, are to be seen, besides 

 here and there those drops of myelin which have remained unabsorbed from the 

 medullary sheaths of the original fibres. On cutting out the central end of the 

 nerve, together with the cicatrix, and separating its fibres, it is seen that the 

 groups of small fibres noticed in the transverse section are continuous with the 

 central ends of the axis-cylinders of the original nerve (fig. 416, D). Either a bunch 

 of small fibres may grow directly from the axis-cylinder of one fibre, or two only 

 may emerge from this ; but these soon bifurcate, and, repeating this process again 

 and again, may eventually form a considerable group. It would appear therefore 

 that the regeneration of a cut nerve is effected by a growth of new fibres from the 

 axis-cylinders of the central cut end, and that many more such fibres are formed 

 in the first instance than the old ones which have undergone degeneration. 

 The growth from the old axis- cylinders always occurs in the situation of a node 

 either the one nearest to the section or one somewhat higher up. The new fibres 

 are at first pale but subsequently acquire a medullary sheath, still later a primitive 

 sheath, with constrictions of Ranvier, which, as in young nerves, are placed at 

 much more frequent intervals than in the old fibres, so that the intervals are 

 much shorter. 



The fibres which grow thus in groups from the old axis-cylinders are often 

 very irregular in their course, twisting around one another, and even looping 

 back in some places for a considerable distance. In the cicatrix especially is this 

 irregularity and obliquity of disposition noticeable, probably on account of the 

 absence here of the guide formed by the sheaths of the original fibres. 



Restoration of function in the nerve may not occur for several months, during 

 which time it may be presumed the new nerve-fibres are slowly finding their way 



