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



whereby the microscopic object is irradiated with incident Hght de- 

 scending through the objective, a special fluorescence opaque iHumin- 

 ator being employed (Brumberg, 11)55). Besides a number of advant- 

 ages of a fluorescence nature in this case, considerable possibilities are 

 laid open by the ability to observe one and the same site of an object 

 simultaneously by phase contrast, dark field and ultraviolet methods 

 and the determination of the character of the absoi'ption. 



FLUORESCENCE MICROSCOPY IN THE VISIBLE SPECTRAL REGION 



Strugger's (1940) observations on the specific behaviour of acridine 

 orange towards healthy, pathologic and dead cells led Krebs (1947), 

 Krebs and Gierlach (1951) and others to use this fluorochrome in 

 radiobiological investigations. It was found in a number of cases, par- 

 ticularly with botanical material, that radiation-damaged cells accu- 

 mulated larger amounts of acridine orange than normal cells and as a 

 result emitted light of longer wave-length (yellow, orange or red). In 

 1953 Strugger, Krebs and CJierlach carried out studies on the early 

 manifestations of injury caused by X-rays in plant cell cytoplasm. 



In 1947 we began our studies which were centred on unicellular 

 plants, cultures of animal cells in vitro and the hemopoietic organs of 

 various animals. In this report we shall attempt to give a generalized 

 survey of the results. 



The first communications (Meissel and Zavarzina, 1947 ; Meissel et al., 

 1951) jDointed out that acridine orange binds diff"erently with the 

 nucleic acids of the nucleus and of the cytoplasm, imparting to these 

 compounds fluorescence of different colour. In 1952 Meissel and Kor- 

 chagin showed, on nucleoproteins isolated from the microbial cell, that 

 deoxyriliose comjDounds form green fluorescent complexes with acxidine 

 orange, whereas under the same conditions this same fluorochrome 

 forms red fluorescent complexes with compounds of the ribose type. 

 These findings, confirmed later by a number of other investigators, 

 made it possible to determine with certainty the distribution and be- 

 haviour of nucleoj^roteins in irradiated cells under vital and supravital 

 conditions. 



The very first reactions towards radiation of cellular nuclei showing 

 a light green fluorescence in the normal condition are manifested in a 

 marked increase in the intensity of fluorescence of the nuclear mem- 

 branes. 



The delicate internal structures of the nuclei harden, the nucleolus 

 and nucleoprotein granules swell, assuming a droplike or pooly apj^ear- 

 ance with increased intensity of fluorescence. It is at that time that a 



