440 



BIOLOGICAL EFFECTS OF RADIATION 



such a case, if the underlying tissues had not been involved the regenera- 

 tion exceeded the normal, because the connective tissue which composes 

 the fin between the two epithelial layers was stimulated, as he thought, to 

 more active growth. Again, he thought that a similar superregeneration 

 might occur, and be similarly explained, when part of the tail was 

 removed by a transverse cut, but he was not sure of this. 



Litschko also investigated the persistence of the inhibitive effects of 

 the irradiation by making the amputations from 1 to 8 weeks after the 



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Fig. 15. — Effects of X-rays upon regeneration of tail in the axolotl. a, dorsal fin on 

 second day after exposure and removal of a portion as shown; 5, normal regeneration of the 

 removed portion, after an exposure without injury to the underlying dorsal musculature, 

 1 month after exposure and operation; c, the same after 2 months showing the normal 

 outline completed although there is still a slight difference between the color of new and 

 old tissue; d, defective healing by scar formation 2 naonths after exposure and operation in 

 a case where the underlying elements of the dorsal musculature were involved; e, super- 

 regeneration 10 months after the exposure and operation;/, tail 2 or 3 days after an amputa- 

 tion that removed only the distal portion of the fin which consists of connective tissue 

 covered by epithelium; g, normal regeneration in such a case 2 months later; h, schematic 

 representation of a more proximal amputation, involving musculature, chorda, and nerve 

 cord, as it appears shortly after the operation; t, superregeneration in such a case 2 months 

 later; j, the same after 9 months. {From Litschko, 40.) 



exposures instead of 1 to 2 hr. after as in other experiments. From these 

 experiments it appeared that the impulse to increased growth of con- 

 nective tissue persisted for a long time when it was once given by the 

 rays. A similar inhibition with stump formation was observed even when 

 the amputation was made 8 weeks after the irradiation, but when the 

 connective tissue tip of this stump was remqved by a second amputation, 

 complete regeneration occurred. This was his final evidence that the 

 power of regeneration was not suppressed as a result of the irradiation, 

 rather the raying was only a hindrance in its expression. 



