416 



BIOLOGICAL EFFECTS OF RADIATION 



interstitial cells survived (Fig. 1, C and D). In correlation with the 

 destruction of interstitial cells, such an individual lost for the time being 

 its power of regeneration ; but the few surviving interstitial cells began to 

 multiply and eventually the power of regeneration was restored. Strelin 

 concluded that destruction of interstitial cells by the X-rays caused loss 

 of the power of regeneration and of budding, and that the data obtained 

 by Zawarzin and himself furnished conclusive proof that the interstitial 

 cells functioned as a reserve of embryonic material from which the other 

 cell types were differentiated. 



Fig. 1. — Microphotographs showing effect of X-rays upon cells oi 1',! inntnhyihn oHgactis. 

 A, from longitudinal section of a normal specimen showing ectoderm, supporting lamella, 

 and part of endoderm. B, from similar section of an irradiated specimen showing no 

 interstitial cells in ectoderm. C, from a 3-day irradiate showing early stage in restoration of 

 interstitial cells from a few such cells that sur^-ived. D, later stage of this restoration. 

 {From Strelin, 62.) 



The results described by these two investigators seem to justify 

 Strelin's conclusions, although it can be argued that the rays affect all 

 the cells of the hydra and so alter the physiological state of the individual 

 as a whole that it becomes temporarily incapable of regeneration, and 

 with heavier exposures its state becomes so much altered that death 

 ensues. Moreover, one is critical of Zawarzin's interpretations where 

 the combination of stimulating and retarding effects is intermingled in 

 the manner described. These results should be thoroughly checked by 

 other workers familiar with the technique of irradiation and the histology 

 of hydras. To prove the case beyond question it would be necessary to 

 produce hydras in which the interstitial cells had all been destroyed and 

 in which the capacity for regeneration as well as that to perform other 



