242 Ross Granville Harrison 



tures already present in the limb at the time of transplantation, or 

 do they grow into the limb from the nerves of the host, guided 

 to their proper place by the structures within the limb ? Obviously 

 the experiment under consideration is not, in itself, sufficient to 

 dispose of the question, though Braus contends, that when we 

 clearly analyze the meaning of the one central fact, that the trans- 

 planted limb contains a typically arranged nervous system, the 

 first of the three possibilities stated by him, /. e.y the formation of 

 the nerves by outgrowth from the center, is to be excluded. 



The results of nerve suturing are dismissed as having no bear- 

 ing on the case, on the ground that there are no nerves present 

 in the limb at the time of transplantation to serve as guide-lines 

 for possible outgrowing nerves. In making this point, however, 

 Braus has failed to note that in normal embryos the nerves reach 

 the immediate vicinity of both the fore and hind limb buds before 

 these appendages are distinguishable." It would, therefore, be 

 impossible to remove a limb bud — and this is especially true ot 

 the fore limb (Fig. i), which Braus used in the majority of his 

 experiments — without including the finer terminal nerve twigs. 

 It would also be impossible to make the incision for implantation 

 without cutting some nerves of the host. Thus in grafting a nor- 

 mal limb upon a normal larva we cannot avoid bringing the cut 

 ends of the nerves of the latter into close proximity to the isolated 

 nerve twigs contained within the former. The two are not actu- 

 ally sutured together, but as Forssmann has shown conclusively, 

 degenerating nervous tissue attracts from a distance the nerve 

 fibers arising from a cut nerve, ^ and the distances in the embry- 

 onic transplantations under consideration are sufficiently minute 

 to fall well within this limit. We must therefore consider that 

 also in these embryonic transplantations guiding nerve twigs may 

 be present, though even were they totally lacking in the trans- 

 planted bud, the nerves of the host would be brought into close 



aneinander geheilt wurden, d. h. also innerhalb der Vereinigungsstelle des Parasiten und Autositen; 

 (3) die Stelle, an welcher das periphere Nervensystem mit dem zentralen, speziell den motorischen 

 Ganglienzellen des letzteren zusammenhangt, d. h. also innerhalb des Autositen.'' Braus '05, p. 442. 



'See p. 253. 



*Forssmann 'q8, 'co. 



