60 



THE MAMMALIAN EGG 



Living rat eggs have also been studied by fluorescence microscopy, 

 involving acridine-orangc staining and irradiation in the near ultra- 

 violet (Austin and Bishop, 1959a; Austin and Amoroso, 1959). In 

 the cytoplasm, only the granular elements fluoresced and these 



wf f H 



Ultra-violet absorption by rat 8-cell egg showing distribution of 

 nucleic acids and nucleotides. X 500. 



showed a brilliant red colour. The red fluorescent granules lay 

 chiefly in the neighbourhood of the germinal vesicle in the oocyte 

 (Fig. 15), but were irregularly distributed in numerous groups 

 throughout the cytoplasm in eggs undergoing fertilization and in 

 2-cell eggs (Figs. 25, 26 and 35). More distinct aggregation was 

 evident in 4-cell eggs, and at the 8-cell stage dense masses of red 

 granules were grouped about each nucleus (Fig. 36). It seemed 

 likely that, under the conditions of these experiments, the red 

 fluorescence was given by mitochondrial mononucleotides. 



Sotelo and Porter (1959) point out that there is good reason to 

 believe that basophilia in tissue cells is located in the small dense 

 particles (Pallade's small granules, ribosomes) which, on isolation, 

 have been shown to contain high concentrations of rna. They 

 found particles of this kind (150 to 200 A in diameter) in the cyto- 



