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



In normal bone-marrow and blood distinct u.v. fluorescence is 

 exhibited by cells of the myelocytic series np to matm'e leucocytes, 

 inclusively; monocytes, megakaryocytes and thrombocytes. Young 

 cells of the erythrocytic series and mature lymphocytes have weak 

 fluorescence. Young lymphocytes (lumphoblasts) in the lymph nodes 

 show clear u.v. fluorescence. 



It is very significant that the fluorescent substance is found chiefly 

 in the cytoplasm of the cells. It is either more or less uniformly distri- 

 buted, or is concentrated for the gi'eater joart in definite regions of the 

 cytoplasm, mostly those adjacent to the nucleus. In vital fluorochrom- 

 ing with acridine orange the substance fluorescing in the ultraviolet 

 partially enters into the composition of the newly-formed granules. 



Cell nuclei, evidently with some exceptions, do not exhibit marked 

 u.v. fluorescence. At times nucleoli may fluoresce and a very faint 

 diffuse fluorescence of the nucleus may be observed. But in these cases 

 also the light emitted by the nucleus is incomparably weaker than that 

 of the cytoplasm ; as a rule the nucleus stands out as a dark object on a 

 bright cytoplasmic background. This is somewhat unexpected. We 

 have already indicated that deoxyribonucleic acid isolated from the 

 cells shows a definite u.v. fluorescence. Evidently when it forms a com- 

 ponent part of the DNA-protein complex deoxyribonucleic acid loses 

 its capacity for fluorescence. 



What is the nature of the substances responsible for the ultraviolet 

 fluorescence of the cytoplasm? By means of special experiments on the 

 selective extraction of various nucleic acid components from the 

 myeloid cells, Brumberg et al., (1960b) showed that they are nucleo- 

 tides, ribonucleic acid and, to a lesser extent, proteins. 



What then are the changes undergone by the u.v. fluorescence of 

 cells subjected to u.v. and ionizing radiation? It was found that as a 

 result of intensive irradiation by u.v. rays (A 250 to 280 m//) or X-rays 

 (in doses exceeding 25kr) the u.v. autofluorescence considerably weakens 

 giving place to clearly visible blue-violet fluorescence, excited by rays 

 of 365 n\fi wave-length. This fluorescence may be studied in an ordinary 

 fluorescence microscoj^e. It appears not only in the cytoplasm but also 

 in the nuclei of the cells. 



The sharp fall in u.v. fluorescence in intensively irradiated cells is 

 due to the resultant photo and X-radiochemical processes leading to 

 labilization of the nucleoproteins and release from the cells of nucleo- 

 tides and nucleic acids. The appearance of a bright visible fluorescence 

 is evidently associated with some kind of structural changes in the 

 nucleoiJroteins and proteins, which have not yet been investigated 

 more closely. 



