176 



REGENERATION 



present in the wound area, therefore. Nevertheless a normal 

 forearm and hand skeleton were formed in the regenerate, 

 whereas in the upper arm the extirpated humerus was not 

 regenerated (Fig. 63). Therefore, the skeleton in the regenerate 

 is certainly not formed by the outgrowing skeleton of the 

 wound; it must have differentiated on the spot from the re- 

 generation material. Weiss has made similar experiments on 

 skin. The same point was illustrated even more clearly in an 

 experiment by Umanski (1938). He irradiated a limb of a black 



Fig. 63. Diagram of fore-limb regeneration in Triton, (a) normal 

 skeleton of the fore-limb; (b) extirpation of the humerus, followed 

 by the amputation of lower-arm and hand; (c) the skeleton of the 

 regenerated lower-arm and hand is normal, but the extirpated 

 humerus is not regenerated. After Przibram. 



axolotl with X-rays, thereby destroying the regenerative 

 capacity of its tissues. The skin of this limb was then replaced 

 by that of a normal specimen of the white axolotl. The limb 

 was thereupon amputated, and regeneration took place. The 

 lack of pigmentation in the regenerate proved that it originated 

 from the grafted skin which had retained its power of prolifera- 

 tion. Similar experiments were made by Trampusch (1951). 

 Instead of skin, he grafted in other cases skeleton or muscle 

 tissue into the irradiated limb. It appeared that in these cases, 

 too, regeneration occurred, and the assumption was again in- 

 evitable that all or nearly all of the material for the regener- 

 ation originated from the implanted healthy tissues. 



The following experiments supply some information on the 



