XI 



THE EFFECTS OF RADIUM AND X-RAYS ON EMBRYONIC 



DEVELOPMENT 



Elmer G. Butler 



Department of Biology, Princeton University, Princeton, N. J. 



Historical. Modifications in early stages of development. Fertilization — Cleavage 

 — Gastrulation. Modifications in later stages of development. Differential sensitivity 

 in embryonic development. Summary. References. 



HISTORICAL 



Many studies have been made during the last thirty years on the 

 effects which radium and X-rays exert on developing eggs and embryos. 

 Two motives appear to have guided investigators into this type of work. 

 First, there has been the desire to investigate, through the use of embry- 

 onic material, the fundamental nature of the alterations which are pro- 

 duced in living cells by exposure to radium and X-rays. For 

 investigations of this type the eggs of aquatic animals are particularly 

 favorable, because of their uniformity and the ease with which they 

 can be obtained in great abundance. Secondly, there have been studies 

 which have been more particularly embryological in character. In these 

 studies radium and X-rays have been used simply as instruments of 

 research. The method of experimental embryology is that of producing 

 abnormal development in order more completely to understand the factors 

 which underlie normal development. For this purpose various mechani- 

 cal and chemical methods have long been employed, and to these has been 

 added the method of radiation. In the following review no attempt will 

 be made to separate these two aspects of the work which has been done 

 on the radiation of eggs and embryos. Indeed, it has often been true 

 that in a single investigation both aspects, the radiological and the 

 embryological, have received equal attention. 



In a survey of the literature dealing with the effects of radium and 

 X-rays on embryonic development one is struck by the scarcity of reliable 

 quantitative data. The work which has been done in this field has been, 

 for the most part, qualitative in nature, and in many cases, particularly 

 in the earlier investigations, the qualitative results are not thoroughly 

 trustworthy. In many cases the amount of radiation which reached the 

 egg or embryo was either unknown or at least unstated, the area of the 

 embryo which came under the influence of the radiation was undeter- 



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