Fig. 131. Two-center effect. Top: "Bridge" of cells and nerve fibeis that has formed between two em- 

 bryonic spinal ganglia of chick (dark areas) cultured in vitro in thin blood plasma membrane. X 48. (From 

 Weiss, '34.) Middle: Regenerated nerve fibers forming "bridges" between "proximal" stumps {a, c) and 

 dislocated "peripheral" stimips (recurrent, b; laterally displaced, d) (from Cajal, '28). Bottom: "Bridges" 

 of Schwann cells that have grown out between the open ends of two fragments of adult rat nerve explanted 

 in a thin blood plasma clot (from Weiss, '52b) . 



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