XII 

 EFFECTS OF X-RAYS AND RADIUM UPON REGENERATION 



W. C. Curtis 

 University of Missouri, Columbia, Missouri 



Porifera. Hydrozoa. Turbellaria. Nemertina. Chaetopoda. Tunicata. Am- 

 phibia. Physiological Regeneration. Discussion. References. 



The prime importance of irradiation in this field is its use as a tech- 

 nique. It is important that the effects of the rays upon regenerating 

 tissues be ascertained in all their morphological, physical, and chemical 

 details, as in other cases where irradiation is used as a means of experi- 

 mentation; but such knowledge waits upon a more extensive under- 

 standing of the effects of these radiations upon protoplasm. In the 

 meantime, one can use the rays in a study of regeneration as one would 

 use stains or reagents in producing results that can be utilized for experi- 

 mentation, without knowing as much as might be desired concerning the 

 manner in which the rays act upon the cells. In a representative series 

 of animals it has been found that exposure to X-rays or to radium 

 reduces or completely destroys the power of regeneration, and in some 

 instances the irradiated individual remains alive for so long a period that 

 its death seems to result from other causes, or at least to be indirectly 

 connected with the irradiation. Healing of the wounded surface usually 

 occurs in a normal manner, while the regenerative changes by which a 

 complete individual is produced are inhibited in proportion to the 

 exposure. In some of these cases the inhibition apparently results from 

 the effects of the radiations upon specific types of cells which are necessary 

 for the regeneration. These cells are either destroyed or changed to such 

 an extent that they cannot function normally ; and such changes observed 

 in cells may be regarded as the obvious, although perhaps not the only, 

 cause for the lost power of regeneration. 



An explanation that suggests itself is the well-known fact of the 

 differential susceptibility of cells to the radiations in question. As 

 formulated in the law of Bergonie and Tribondeau, undifferentiated germ 

 cells, embryonic cells, and the less differentiated cells of adult animals 

 are more susceptible to X-rays and to radium than more differentiated 

 cells. If regeneration involves the presence of cells with embryonic 

 potencies, which respond by division, movement, and differentiation and 

 so restore the normal whole in a mutilated animal, or from a fragment, 



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