REGENERATION 423 



In his extensive study of the effects of radium irradiation upon 

 Polycelis nigra, and comparisons with Planaria torva and Planaria lugubris, 

 Weigand (67) has considered both the gross and the histological changes 

 involved. As a source, Weigand used a radium bromide preparation 

 containing about 15 mg. and enclosed in a steel capsule mth a mica 

 window 10 mm. in diameter. For longer periods the planarians were 

 exposed three at a time in a glass container 4 mm. deep and 10 mm. wide 

 and covered with thin aluminum foil. The container was filled with 

 water and placed directly on the mica window of the capsule. For the 

 exposures of 5, 10, and 15 min. a block of paraffin with a similar cavity 

 was used. This procedure seemed not to result in a lack of oxygen or an 

 undue increase of temperature, except in a few instances. 



The experiments included exposures ranging from 5 min. to 16 hr. 

 and the period of observation ranged from 6 to 27 days between the begin- 





^'4 





,.__ riVe. IfTgc 11 Tgc. r, Tyc. s Tge. -Jige. 



Fig. 6. — Concrescence in wound region of head and tail pieces of Polycelis nigra exposed 

 to radium and cut immediately after. 7 Tge., etc., days after such exposure and operation. 

 {From Weigand, 67.) 



ning of the experiment and death or fixation of the individual specimens. 

 In all the experiments on regeneration the worms were cut transversely, 

 through the region of the pharynx, into head and tail pieces. When 

 alive, the head pieces showed the typical cap of regenerative tissue at the 

 cut surface and the new mouth, which could be compared in controls and 

 in the irradiates; but the regenerated pharjoix could be identified only as 

 it happened to be thrust from the mouth opening. The tail pieces showed 

 the new tissue with its subsequent development of eyes and typical head 

 outline, the mouth, and the pharynx only when extruded. For other 

 details sections were necessary. 



In Weigand's first experiment Polycelis nigra was variously exposed 

 and in each case cut immediately after the exposure. It was found 

 that the rays did not have a lethal effect, within the period of observation 

 (13 to 21 days), if exposure did not exceed 15 hr., as in this experiment, 

 although the specimens that were exposed more than 15 m.in. showed 

 characteristic concrescence of the margins and other deformations that 

 eventually prove lethal (Fig. 6). All the irradiated pieces began to 

 regenerate, at least the wound healing was completed. The amount of 

 regenerative tissue that could be seen externally as the "cap" diminished 

 with increased exposure and the regeneration became correspondingly 



