122 M. N. MEISSEL, E. M. BRUMBERG, T. M. KONDRATJEVA AND I. J. BARSKY 



distinguished by a highly brilHant u.v. autoflnorescence (Fig. 9). The 

 substance responsible for this fluorescence is nucleoprotein modified in 

 a sj)ecific manner and firmly attached to the cellular substrate from 

 which it is separated with difficulty. 



We also observed enhanced fluorescence in irradiated animal cells 

 continuing their growth and metabolism on cultivation in vitro. This 

 was observed already after a dose of 100 r and attained a maximum 

 at doses of 2,000 to 3,000 r (Fig. 10). Further increase in dosage led to 

 a diminishing of the u.v. fluorescence and at 25 to 30 kr it became 

 extinct giving place to higher wave-length emission, in the visible 

 region. 



The increase in the ultraviolet fluorescence of irradiated (with 

 moderate doses) cells continuing to metabolize parallels the accumu- 

 lation in them of nucleotides and ribonucleic acid and these processes 

 are presumalily intimately connected. The newly-formed RNA obvi- 

 ously differs from the normal one. In certain types of cells (for instance 

 HeLa cells) after irradiation marked u.v. fluorescence ajjpears in the 

 nucleoli. 



It should be stressed that cells irradiated with X-rays and continuing 

 their metabolic activities are highly susceptible to irradiation by short 

 u.v. waves. Such irradiation very quickly leads to extinction of u.v. 

 fluorescence and to the appearance of longer wave visible fluorescence. 

 We observed this in cultures of monkey kidney cells in vitro irradiated 

 with doses beginning from 100 r. 



In irradiated yeast cells {Endormjces magnusii) continuing to meta- 

 bolize on a nutrient medium we observed a well-defined u.v. auto- 

 fluorescence of the nuclei. In non-irradiated cells the nuclei as a rule 

 do not exhibit fluorescence (Fig. 11). This is the only case we have 

 observed of the appearance of u.v. fluorescence in the nuclei of irradi- 

 ated cells. 



CONCLUSIONS 



1. Vital and supravital fluorochroming followed by observation in 

 the fluorescence microscope permits detection of the early stages of 

 impairment in the nucleoproteins of cell nuclei beginning immediately or 

 soon after irradiation. These are revealed as a result of the changes in 

 the natui'e of the complex formed between diaminoacridine fluoro- 

 chromes and structurally damaged DNA proteins, affecting the in- 

 tensity and colour of the fluorescence of the newly-formed com])lexes. 

 The nature of such structural impairments is not yet com])letely eluci- 

 dated. Possibly labilization and broakdo\\ n of tlie DNA linkage with 



