REGENERATION 



447 



Fig. 20.— Effect of X-rays (15,000 r) 

 upon regeneration of hind limbs of Triton 

 cristatus. a, ventral ^^ew 119 days after 

 exposure of the right and amputation of 

 both hind limbs; b, ventral view of a 



The effect of the irradiation could not be entirely local, since it was 

 found that with local exposures the effects became evident to some degree 

 in the regeneration of the unexposed extremity of the same animal 

 (Fig. 22). With weaker exposures the nonirradiated limb, or "regenerate 

 control," developed in about the same 

 manner as any " normal control." No 

 evidence was found of any directly 

 stimulating action of the rays upon 

 the regeneration. There is nothing 

 in this paper regarding the histological 

 changes in controls or in irradiated 

 individuals. 



In another paper (52) these same . ., ^^ ^ 



similar specimen 62 days after a second 

 mvestlgators have studied the effects amputation of both limbs. (From Brunst 



of X-rays upon regeneration of the ""'^ Scheremdjewa, 6.) 

 tail in Pelobates fuscus tadpoles that were given single exposures ranging 

 from 750 to 7500 r (Fig. 24). Within these limits they obtained all stages 

 in the inhibition of tail regeneration. It was found that total exposures 

 had a greater effect than local exposures of the same order. The dorsal 

 side, which was toward the source of the irradiation, showed greater 

 injury than the ventral, as seen either in greater inhibition of the 

 dorsal regeneration or in more intensive reduction on the dorsal side of 

 the stump (Figs. 25 and 26). The tail outline became asymmetrical 

 in the first case, because the tail of the regenerate was bent dorsally; and 

 in the second, because the ventral part of the stump predominated. The 



optimum exposure, of those 



employed, for this dorsal 

 bending was 1500 r after which 

 the ventral regeneration was 

 still quite intensive. With 

 TT oi TTo- . . ^' /o-7cn N 2250 r the entire tail regen- 



FiG. 21. — Effect of X-rays (3750 r) upon regen- . «• , i 



eration of hind limbs of Triton cristatus. a, ventral CratlOU WaS SO affcctcd that 



\'iew 135 days after exposure of the right and amputa- ^J^g beildillff Was leSS in evi- 



tion of both hind limbs; b, ventral view of a similar rnu j re 



specimen 135 days after; c, ventral ^^ew of a similar denCC. The different tissUCS 



specimen 74 days after a second amputation of both q( iUp. fail and of the stumn 



limbs. (From Brunst and Scheremetjewa, 6.) i i i /-<• 



showed differing sensitivities 

 to the rays and morphological injuries that could be clearly recognized 

 appeared in the following order: (a) pigment cells; (6) epithelium; 

 (c) chorda; (d) gelatinous connective tissue; (e) musculature; (/) nervous 

 tissue. The regenerative potencies of the tissues were lost in this order : 

 (a) chorda; (6) spinal cord and musculature; (c) gelatinous connective 

 tissue; (d) blood vessels and epithelium. The differing sensitivity of 

 chorda and spinal cord was especially noticeable. In spite of the fact that 

 the spinal cord was nearer the source of the rays, it grew intensively after 



