Ex pen nif tits in Tratisplatitnig Limbs 243 



proximity with the latter, while it is still nothing but a small nodule 

 of mesenchyme cells, and there is no reason to suppose that these 

 nerves would have any more difficulty in making proper connec- 

 tions, than the nerves have in growing into the natural limbs. 

 It would therefore seem to be almost immaterial from the stand- 

 point of the outgrowth theory whether nerve twigs are present in 

 the limb at the time of transplantation or not, and my own ex- 

 periments show that this is actually the case.^ 



Braus nevertheless finds an insuperable objection to the accept- 

 ance of the outgrowth theory in the fact that the grafted limb is 

 entirely new territory for the nerve, where we should not be justi- 

 fied in supposing the latter to be able to find its way. But this 

 difficulty would be real, only in case it could be shown that the 

 nerve fibers going to each organ are specific, /. e., that the mode of 

 branching of the fibers is determined in the nerves themselves. 

 While it may be true that there are some specific differences between, 

 for example, muscular and cutaneous nerve fibers, there is no evi- 

 dence to show that the nerves running to any particular muscle 

 are different from those supplying other muscles. In fact our 

 experience with nerve anastomosis shows that the contrary is the 

 case. There is no difficulty, therefore, in the supposition that, 

 if the structures in the fore limb normally direct the course of the 

 nerves of the brachial plexus, they may direct equally well the 

 lumbo-sacral nerves, when, as in the case of the transplantations, 

 the fore limb is placed in the way of t .e latter. 



Braus supports his contention mainly upon the supposed anal- 

 ogy with the behavior of the rudiment of the lateral line organs 

 in development, but in so doing he has partially mistaken the 

 meaning of my experiments which he cites. ^" While these experi- 

 ments did show that the rudiment of the sense organs — the nerve 

 itself is merely drawn along with them — does not grow except in 

 normal paths or paths similar to the normal ones, they did not 

 prove that the vagus organs, for instance, could not grow into 

 the supra-orbital path, as would have to be the case were the anal- 

 ogy with the strange nerves in a transplanted limb to hold. In 



^See pp. 256 and 269. 

 ^'Harrison '03. 



