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



animals (Meissel, 1957; Meissel et al., 1958). They result largely from 

 the direct action of the radiation, since screening of the hemopoietic 

 organs obviates the reaction to a considerable degree. The aforemen- 

 tioned nuclear impairments revealed by fluorescence microscopy were 

 discovered soon after iiTadiation in leucocytes and lymphocytes of the 

 peripheral blood vessels (Kondratjeva) and also after iri-adiation of 

 blood in vitro (Kondratjeva and Pinto, 1961). 



In the cytoj)lasm and small vacuoles of the cell acridine orange com- 

 bines with the nucleic acid and nucleotides to form complexes showing 

 a bright red fluorescence. This fluorochrome binds not only with 

 existing (pre-formed) granules but also forms new ones as a result of 

 the separating out of the dye-nucleic acid complexes. 



Considerable amounts of nucleic acid compounds are observed to 

 accumulate in the cytoplasm of irradiated cells. These compounds form 

 with acridine orange numerous large and small granules showing a fiery 

 red fluorescence. The large granules, or at least some of them, are dis- 

 tinguished by greater density and stability than the granules of un- 

 irradiated cells. They do not spread out under the action of various 

 factors, including u.v. irradiation. The change in the nature of the cyto- 

 plasmic granules in the irradiated cells is indicative either of physico- 

 chemical changes in the nucleic acids forming complexes with acridine 

 orange or else of the formation of a stronger bond between these sub- 

 stances and the proteins of the cytoplasm. 



Irradiated cells continuing their metabolic activities accumulate in- 

 creasing amounts of nucleotides and ribonucleic acids in the cytojDlasm, 

 in a number of cases completely filling up the cells. This pertains 

 equally to cells in vitro and in vivo, for instance the myeloid cells of the 

 bone-marrow. It is interesting that in the cytoplasm and vacuoles of 

 irradiated metabolizing yeast cells also basophilic substances and volu- 

 tin accumulate, representing a complex of ribonucleic acid and poly- 

 phosphates. Hence retardation of the metabolism of nucleotides and 

 other high energy compounds is a quite widespread reaction of irradi- 

 ated cells, belonging to the most varied cellular types. 



ULTRAVIOLET FLUORESCENCE 



Many biologically important sul)stances (aromatic amino acids, 

 proteins, purine and pyridine bases, nucleotides, nucleic acids and some 

 vitamins) possess absorption maxima in the u.v. region. In consequence 

 one might exjiect that fluorescence of these substances could also be 

 exhibited in the same spectral region. For a number of substances this 

 has proved to be the case. 



