424 SCIENCE PROGRESS 



has supported in a veiy conclusive and entirely independent 

 way the view that Mott and I advanced some years ago of the 

 value of the neurilemma in maintaining the nutrition of the axis 

 cylinder. There is but little doubt also that these cells act 

 as phagocytes in the removal of the degenerated products of 

 the other portions of the nerve fibre. But after this is accom- 

 plished they elongate and unite into long chains. It is this 

 appearance that has led some observers into regarding them 

 as true nerve fibres ; they have jumped to the conclusion that 

 the neurilemmal cells are also able to form a conducting core, 

 and so have regarded auto-regeneration as a histological possi- 

 bility. But all recent observations by the best methods, as I 

 have already stated, have failed to discover either an axial 

 core or a fatty sheath in these " embryonic fibres " as they 

 have been termed. Howell and Huber put it very well nearl}^ 

 twenty years ago when they said the peripheral structures are 

 able to prepare the scaffolding, but the axon, the essential 

 conducting core of the fibre, has an exclusively central origin. 



The change in the neurilemmal cells vdiich occurs in the 

 peripheral segment is even more vigorous at the central ter- 

 mination of the cut nerve ; here its nutritive function (or 

 apotrophic function, as Marinesco calls it) is effective, and 

 provides for the nourishment of the actively lengthening axis- 

 cylinders. At the peripheral end, unless the axons reach it, it 

 is ineffective in so far as any real new formation of nerve fibres 

 is concerned. If, however, the axons reach the peripheral 

 segment, the work of the neurilemmal cells has not been useless,, 

 for they provide the supporting and nutritive elements necessar}^ 

 for their continued and successful growth. Moreover, the neuri- 

 lemmal activity appears to be essential. In the white fibres 

 of the central nervous system the neurilemma is absent ; in this, 

 situation not only is the removal of the products of degeneration 

 a very slow process, but, as I have previously mentioned,, 

 regeneration does not occur. 



Having now considered the manner in which nerve regene- 

 ration occurs as elucidated by experiments upon animals, we can 

 next pass to a study of the problem in man. When the accident 

 is a slight one, or when a surgeon during an operation 

 necessarily divides a number of small cutaneous and similar 

 nerves, the process of repair may be confidently left to nature. 

 But when a large nerve trunk is divided, the case is a difterent 



