SUSCEPTIBILITY OF AMPHIBIAN OVA TO X-RAYS 423 



ians is due not onlj' to multiplication and differentiation of cells 

 but also, apparently, to tissue redifferentiation (morpholaxis- 

 Morgan) it would appear that the power of differential morpho- 

 genesis, even when not accompained by cell division, may be dis- 

 turbed by irradiation. In the experiments mentioned, however, 

 the chief effects of the rays seemed to be the inhibition of the 

 formation and differentiation of new tissue. By exposing triton 

 larvae to radium Schaper inhibited the regeneration of the tail 

 and limbs. The wounds healed and a mass of cells accumulated 

 in the region of the lost parts but no specific regeneration took 

 place. Here the power of simple cell reproduction was not com- 

 pleteh' inhibited, although the power of differentiating new tissues 

 was destroyed. In the human skin exposed to the X rays one 

 sometimes finds the Malpighian layer greatly thickened. Here 

 again there appears to be an interference with differential morph- 

 ogenesis, although not at first of cell multiplication. In the skin of 

 mice exposed to radium G.Guyot,('09)describes at first an increased 

 activity in the multiplication of the cells of the Malpighian layer. 

 Here, apparently, all the daughter cells undergo involution in- 

 stead of only part, as in the normal skin. The reserve supply 

 of genetic cells is thus used up and with the completion of involu- 

 tion in these cells the skin becomes denuded of epithelium. 



The effects of irradiation on simple reproductive morphogenesis 

 may be most conveniently studied in unicellular organisms. Ex- 

 periments with these show that as a rule they are relatively very 

 resistant to the X rays or to radium. Thus neither Paramoecia 

 aurelia nor Paramoecia caudatum showed any difference in form 

 or in rate of division when exposed twelve hours to Roentgen 

 rays, although 15 minutes exposure of toad eggs undergoing 

 cleavage to these rays inhibited gastrulation. Schaudinn '99, 

 has shown, however, that some species are decidedly susceptible. 

 Zuelzer ('05) has likewise described injurious effects which 

 long exposure to radium causes in some protozoa. Bacteria are 

 relatively resistant to theXrays although Rieder, and others, have 

 described some inhibition of growth when the exposure was very 

 intense. Similar effects have been described when bacteria 

 are exposed to radium (Koerniche). The relatively great resis- 



