Experiments in Transplanting Limbs 241 



4 It happens not infrequently that the transplanted extremity does not remain 

 single, but gives rise to a second limb which is the mirror image of the original one. 

 This accessory limb is at first small but after a time may overtake the original 

 one in development. Such supernumerary limbs may also be formed after irreg- 

 ular amputations or mutilation of the limb rudiment in normal tadpoles,"" in which 

 case the nerves as well as the other structures are typically developed. On the 

 other hand, when the supernumerary limb develops from a transplanted bud, Braus 

 finds that nerves are totally lacking within it, as indicated both histologically and 

 by the failure of such limbs to respond to electrical stimulation. 



Aside from these main points Braus' papers contain a wealth 

 of interesting and important observations. His conclusions are 

 however, interwoven with his statements of fact and are presented 

 in the form of a continuous argument, thus rendering it difficult 

 to bring effective criticism to bear upon the work. Nevertheless, 

 by first admitting the facts to be true, we may take up the thread 

 of the argument and, I think, conclusively show that it does not 

 constitute a logical proof of the continuity theory, but is merely 

 to be regarded as a possible interpretation, in which analogies and 

 collateral facts of uncertain relevance play a large role. The same 

 facts may be interpreted quite as readily, if not more so, in accord- 

 ance with the outgrowth theory. The experiments do not approach 

 the problem directly enough to determine questions of histogenesis, 

 and there are too many loopholes left to permit of a rigid proof. 

 In the experimental part of the present paper it will be further 

 shown that the facts which are most important for Braus' argu- 

 ment are not of general validity. 



In considering the experiments just referred to under the first 

 heading, Braus attacks the question as to the origin of the nerves in 

 the transplanted limbs." Are the nerves developed out of struc- 



^Barfurth '94; Tornier '05. 



'Braus states this problem in somewhat different form: "Um dies zu erlantern, mbchte ich zunachst 

 die Frage zu beantworten versuchen: an welcher Stelle verbindet sich bei meinen Kompositionen die 

 motorische Bahn des Autositen mit derjenigen des Parasiten ? 



* * * Es miisste deshalb auf der ganzen Ausdehnung der motorischen Bahn nach der 

 Verwachsungsstelle gesucht werden; doch kommen naturgemass auf dieser 3 stellen hauptsachlich 

 in Betracht: (i) die Stelle, an welcher die peripheren Nerven mit den Muskeln der transplantierten 

 Gliedmasse in Verbindung stehen, d. h. also innerhalb des Parasiten; (2) die Stelle, an welcher die 

 Einpfropfung erfolgte und wo primiir bei der Operation dieGewebeder beidenverwendeten Embryonen 



