Experijuents m Trans pi antnig Limbs 247 



bility, that in the case which Braus cites the relative size of the 

 different parts of the nerve trunk was the same in the earher 

 stages of development as when finally enumerated. I have not 

 found in any of my experiments such marked differences in size 

 between the intrinsic and extrinsic portions of the nerves as Braus 

 found in the case figured ;^^ and there may even be no enlargement 

 at all. Furthermore, sudden thickening of the nerve trunks do 

 not take place exclusively at the point where they enter the limb 

 but may take place at any dividing point within the limb. 



In this connection it is interesting to note that the exact enumer- 

 ation of the nerve fibers in the hind legs of adult frogs, made by 

 Dunn, shows that the number of medullated fibers increases as 

 the periphery is approached.^* This increase is not confined to 

 the finer nerve twigs but begins to manifest itself in the sciatic 

 nerve where Dunn finds that the increase is from 6 to 8 per cent. 

 This is due to bifurcation of fibers; branching fibers of large cali- 

 ber were actually observed in teased preparations. When, there- 

 fore, we explain the peripheral enlargement of the nerves as they 

 enter the transplanted extremities as due to division of the axones 

 and not, as Braus holds, to the existence of fibers having no con- 

 nection with the center, we are calling into consideration a con- 

 dition which differs from the normal merely in degree, not in kind. 

 This view is, in other words, in accordance with known tacts relat- 

 ing to the peripheral distribution of nerves, while the explanation 

 given by Braus can at best be regarded as an uncertain hypothesis. 



The fourth point which Braus makes is of somewhat the same 

 nature as the second, and is considered by him as showing that 

 the origin of the nerve fibers is to be sought in a much earlier stage 

 of development than that in which either the cell outgrowth theory 

 or the cell chain theory of Balfour place it.^^ It is maintained that 

 no nerves are formed in the accessory limbs which often arise 

 from the transplanted buds, and that this is a distinct confirma- 

 tion of the argument against the outgrowth theory, because this 



"Braus' 05, Fig. 12A, p. 454. 



i^This was pointed out by Professor Donaldson in the discussion which followed the reading of my 

 communication before the British Medical Association. 

 '^Braus '05. p. 460. 



