J\fo. 4 Interphase nucleus of mouse spleen cell in culture (o) living (b) fixed 

 and Feulgen-stained. In (b) the chromocentres are prominent; those which 

 are not obscured by the nucleoli in (o) are seen in the same position in both. 

 X 2400 (reduction 3/4). 



No. 5 (a) Two interphase cells in culture of chick osteoblasts to illustrate 

 the effect of 12-5 millimolar adenosine on the nucleoli. X 2000 (reduction 

 3/4). (b) 14 minutes after (a), (c) 37 minutes after (0). (Some effect on the 

 nucneoli is seen at much greater dilutions.) 



