422 CHARLES RUSSELL BARDEEN 



cessfully in reducing secretion of the sweat glands in mjin (Pusey). 

 The mode of action in these cases is uncertain. 



It is undoubtedly the morphogenic protoplasmic activities 

 which show the chief effects of exposure of living things to the 

 X rays or to radium. These morphogenic activities may be 

 subdivided into reparative, reproductive and differential or evo- 

 lutionary activities. The reparative activities have to do with 

 the restitution of worn or injured structures; the reproductive, 

 with the multiplication of like individuals; the differential, with 

 the organization of daughter individuals varying in structure 

 to a greater or less extent from that of the parents. Unicellar 

 organisms multiply largely by simple reproductive morphogenesis, 

 while the cells in the bodies of multi-cellular organisms undergo 

 extensive, though specifically determined differentiation. In 

 some tissues, as in the nervous system, cell differentiation may 

 lead finally to a loss of reproductive power, although not to a loss 

 of reparative potentiality. In other tissues, as in the epithelium, 

 the bone-marrow and the generative epithelium of the testicles, 

 cell multiplication accompanied by specific differentiation of 

 certain of the daughter cells continues through life. 



The various types of morphogenesis, the reparative, repro- 

 ductive and differential, do not seem to be equally susceptible 

 to the X rays. 



I know of no experiments made to test the effects of exposure 

 on reparative activity unaccompanied by a reproductive or 

 differential cellular morphogenesis. The test could most easily 

 be made by removing a part of the body of a unicellar organ- 

 ism and then exposing it to the X rays. Since most unicellar 

 organisms, even after prolonged exposure, readily multiply by 

 fission and the daughter cells have no apparent difficulty in assum- 

 ing the parent form it would seem probable that such organisms 

 would be able to regenerate lost parts after exposure to the rays. 

 In multicellar organisms, the power of regeneration may be inhib- 

 ited by exposure to the rays. Thus Bardeen and Baetjer ('04) have 

 shown that exposure to the X rays inhibits the power of regener- 

 ation in fresh-water planarians; and Schaper ('04), that exposure to 

 radium produces similar effects. Since regeneration in planar- 



