FLUORESCENCE STUDIES OF NUCLEOPROTEINS 109 



characteristic separation of the nucleoproteins into two fractions begins 

 to make its appearance. One fraction weakly flnorescent, lias a green 

 colour and the other fluoresces with a more 1)rilliant, whitish light. At 

 first the latter fraction is in close contact with the former, but gradually, 

 evidently turning more fluid, it becomes mobile, circumventing the 

 larger nuclear structures, nucleoli, nucleoprotein granules and the 

 internal surface of the nuclear membrane. 



The next stage is a sharper differentiation of the nuclear material. 

 The amount of the brilliant white fraction increases, forming droiDlike 

 accumulations that assume a greenish yellow colour and are often to be 

 found touching the membrane. At this stage one may observe nodal 

 enlargements of various shapes. At times this is accompanied by partial 

 secretion of the brilliant white nucleoprotein fraction from the nucleus. 

 The nuclear membrane becomes markedly thicker and begins to 

 fluoresce with a yellowish green colour. The nuclear structures become 

 undifferentiable. In separate areas of the nucleus may be found accumu- 

 lations of the more fluid brilliant fraction in the form of two or three 

 pools or droplets. In the next stage the nuclei disintegrate and in their 

 place remain variously shaped accumulations of highly fluorescent 

 brilliant white substance. 



We believe that the changes observed in the nuclear matter are 

 associated with the various stages of denaturation of DNA-protein, 

 with its labilization and with the separation of DNA from the protein. 

 The initial stages of DNA-protein denaturation are evidently accom- 

 panied on increase in complex formation with acridine orange with a 

 resultant intensification of the fluorescence of the complex. The sej^ara- 

 tion of DNA from the protein is characterized morphologically by the 

 appearance in the nuclear chromatinic structures of a substance exhibit- 

 ing a bright whitish-green fluorescence. Further intensiflcation of the 

 fluorescence and a shift of the colour in the longer wavelength direction 

 is accompanied by liquefaction of the substance (clearly seen in the 

 microscope), and by a fall in viscosity, as a result of which the substance 

 flows around the nuclear structures, forming drops and pools. In this 

 way vital fluorochroming of the irradiated cells allows one to observe 

 directly the various stages of denaturation and depolymerization of 

 DNA-protein. 



Such in general are the impairments in the nucleoprotein structures 

 of the nucleus proceeding at various rates depending upon the dosage 

 and upon the time elapsing after the radiation, as well as upon the radio- 

 sensitivity of the cells. A highly interesting effect, brought to light only 

 with the aid of fluorescence microscopy is the change in the nature of 

 the fluorescence of the damaged cell nucleus, a considerable increase in 



