194 Charles Russell Bardecn, M. D. 



entiation as upon cell-reproduction. The spreading out of the 

 surface epithelium so as to cover a cut surface, whereby columnar 

 epithelium becomes transformed into pavement epithelium also 

 indicates this. Death in exposed specimens may possibly be due 

 to a necessity on the part of the organism for a certain amount 

 of cell-reproduction. 



The effects of the Roentgen rays on planarians thus tend to 

 support the view of those investigators who regard its effects 

 upon the tissues of other animals as due primarily to its action 

 on cells capable of reproductive activity. Scholtz in his excellent 

 clinical and experimental studies on the effects of X rays on the 

 mammalian skin^ concludes that both the nuclei and the cell- 

 protoplasm of the epithelial cells are injured by the rays, but 

 that the effect on the connective tissues, elastic tissue, muscu- 

 lature and cartilage is very slight if any. The skin on both sides 

 of a rabbit's ear may be affected when it is exposed to rays on one 

 side only. 



The effect is not, however, a direct one upon the actual process 

 of cell-division. This is shown in planarians by the production 

 of tissue at a cut surface during the first few days of exposure 

 to the rays. It is indicated also by the work of Gilman and Baet- 

 jer on chick embryos^ which showed that exposed hen's eggs 

 develop even faster than control eggs for a few days although 

 subsequently development is markedly altered and checked. 

 One of us, likewise, found that exposure to Roentgen rays re- 

 peated frequently throughout the day for several days failed to 

 prevent the normal course of development in the eggs of certain 

 sea-urchins and teleosts during the peroid of exposure. The 

 latent period between exposure to the rays and the development 

 of a burn is well known to clinicians. 



1 "Ueber den Einfluss der Roentgenstrahlen auf die Haut in gesunden und 

 kranken Zustande," Archiv f. Dermatologie und Syphilis, LIX, pp. 87, 241, 421, 

 X902. 



^ Some effects of the Roentgen rays on the development of embryos, Amer- 

 ican Journal of Physiology, X, p-. 222, 1904. 



