Vol. XXVII. August, 1914. No. 2 



BIOLOGICAL BULLETIN 



THE EFFECT OF X-RAYS ON THE RATE OF CELL 

 DIVISION IN THE EARLY CLEAVAGE OF 



PLANORBIS. 1 



A. RICHARDS. 



Only a very short time had elapsed after the announcements of 

 the discovery of X-rays (in 1895) and of radium (in 1898), when 

 it became generally known that animal and plant life can be pro- 

 foundly affected by radioactivity. Subsequently, a large amount 

 of experimentation has been done and many interesting results 

 prove the powerful action of these agents upon living matter. 

 Physiological and therapeutic studies of radioactivity have long 

 since given a firm empirical foundation for its application in the 

 cure of disease. From the pure biological standpoint, also, 

 experimentation has not been lacking; instead, a long list of 

 titles stands to its credit. 



However, most of this purely biological work has concerned 

 itself with the production of abnormalities either in the embryo 

 or in the adult. Only recently has there been any attempt to 

 analyze these results from the study of the units which make 

 up the tissues affected. Nevertheless, it seems clear that the 

 effects upon an organism of radioactivity, or of any agent which 

 produces abnormalities, must depend very largely for any real 

 explanation on results obtained from the study of the effects 

 of that agent upon the cellular elements making up the organism. 

 In the present cases the character of the animals studied accounts 

 for the lack of data at hand upon the more detailed effects on the 

 cells of the tissues in question. Generally vertebrates have been 

 chosen as subjects of experiment and observation and their cells 



1 Contribution from the Zoological Laboratory of the University of Texas, No 

 117. 



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