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SENESCENCE AND REJUVENESCENCE 



occur in such cases and that the regeneration takes its origin from 

 cells or parts of cells which have never undergone differentiation, 

 so that even in these cases development is progressive, not regres- 

 sive. His conclusions are based on the histological appearance, 

 not upon the behavior of the cells. One of the cases cited by him 

 as an example is the regeneration of striated muscle after injury. 

 He points out that the only portions of the muscle which take part 

 in the regeneration are the nuclei and the small accumulations of 



FIGS. 1 1 7-122. Various stages of regeneration after wounding in striated muscle: 

 Fig. 117, injured muscle after three days, showing proliferation of nuclei and formation 

 of protoplasmic cells; Fig. 118, multinucleate masses resulting from proliferation; 

 Figs. 119, 120, "muscle buds" at ends of injured fibers; Fig. 121, regenerated fibers; 

 Fig. 122, giant cells, inclosing a piece of necrotic muscle fiber. From Ziegler, '01. 



granular undifferentiated cytoplasm, as he terms it, which surround 

 them. From these parts the new muscle cells arise by division of 

 the nuclei and growth of the granular cytoplasm (Fig. 117); these 

 cells form multinucleate masses either along the course (Fig. 118) 

 or at the injured end of the fibrillar substance (Fig. 119). From 

 the cytoplasm of these cells new fibrillar substance arises in con- 

 tinuity with the old (Figs. 120, 121). When these cells are not in 

 contact with living muscle substance, as at b in Fig. 117, they form 



