THE EFFECT OF ULTRA-VIOLET LIGHT RAYS UPON 

 THE DEVELOPMENT OF THE FROG'S EGG. 



W. M. BALDWIN, 

 DEPARTMENT OF ANATOMY, UNION UNIVERSITY (ALBANY MEDICAL COLLEGE). 



Ij THE ARTIFICIAL PRODUCTION OF FOLDED (U-SHAPED) 



EMBRYOS. 



This paper is the second of a series dealing with an investiga- 

 tion of the nature and mechanism of causation of certain ab- 

 normal, developmental results obtained by raying certain re- 

 stricted areas of the fertilized ovum of the frog by means of 

 ultra-violet light rays. Since the first paper dealt with the pro- 

 duction of a single type-defect, spina bifida, the possibility of 

 production of another constant and fixed experimental result, 

 a folded or U-shaped embryo, justifies the separate consideration 

 of that result in this contribution. Once again the value of the 

 physical method of attack upon the complex problem of de- 

 velopmental reaction is demonstrated. In this problem we are 

 concerned with a readily controllable and constant, causative 

 agent on the one hand and a uniform embryological defect on 

 the other. This one technical condition permits of a more 

 thorough analytical inquiry into the mechanism of production 

 of this developmental defect. In addition to this consideration, 

 however, as is to be expected the experiment gives further insight 

 into the genetic constitution of the fertilized, undivided ovum, 

 and, more specifically, helps in the identification and location of 

 the organ forming substances and anlagen. The apparatus used 

 for the experiment was that detailed in the preceding paper. 

 Some of the work was done, however, with an apparatus for 

 the use of which I am indebted to Mr. W. S. Andrews, of the 

 General Electric Company at Schenectady. With both forms 

 of apparatus, the surface area concentration of the rays was 

 increased through the' use of convex quartz lenses. 



The eggs used were those of the common species of frogs found 



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