4 Charles Russell Bardeen 



tropism toward the Roentgen rays, and that the protoplasm of 

 Paramecia seems injured by the rays. I have found paramecia 

 very resistant to the Roentgen rays. Twelve hours' exposure to 

 powerful rays made no difference in the form or rate of division 

 in P. aurelia or P. candatum. Exposure to the rays seemed not 

 to influence conjugation. M. Zuelzer in protozoa which were 

 exposed to radium rays under the microscope noted primarily 

 an injury to the nuclear substance. The cytoplasm appeared 

 affected later than the nuclei. Great variation in susceptibility 

 was noted in different species. Zuelzer gives a brief summary of 

 the previous literature on this subject. 



Zuelzer" found insects, and Danysz^- insect larvae affected by 

 radium rays. 



The action of Roetgen and radium rays on the fertilized eggs 

 of Ascaris megalocephala has been studied by Perthes. ^^ Perthes 

 found that there is a retardation of the cleavage of eggs exposed 

 to the rays and that the later divisions are either inhibited or are 

 abnormal. In the latter case the eggs give rise to either irregular 

 masses of cells or to abnormal embryos. The effects depend 

 largely on the degree of exposure. The nuclei of the exposed eggs 

 are markedly affected. The chromosomes of the dividing nuclei 

 are irregular in shape and sometimes seem to be divided abnor- 

 mally into smaller parts. The spindle figures appear normal. 



In fresh water Planarians Bardeen and Baetjer^^ showed that 

 exposure to the Roentgen rays destroys the power of regeneration. 

 Schaper^^ has shown that exposure to radium rays produces sim- 

 ilar effects. 



The action of Roentgen rays on the developing eggs of sea- 

 urchins was found to be negative by G. Schwarz." In the spring of 

 1903 the writer failed to get any positive results on exposing the 

 eggs of sea-urchins and teleosts to the Roentgen rays, but these 



M. Zuelzer: Archiv fiir Protistenkunde, v, p. 358, 1905. 

 ^^Danysz: Compt. Rend., cxxxvi, 1903. 



^'Perthes: Archiv fiir klinische Chirurgie, Ixsi, 1903; Deutsche med. Wochenschrift, Nr. 

 17-18, 1904. 



^^Bardeen and Baetjer: This journal, i, p. 192, 1904. > 



^^Schaper: Anat. Anzeiger, sxv, p. 298, 1904. 



'^G. Schwarz: Wiener klin. Wochenschrift, xvi, s. 714, 1903. 



