DEAN B. COWIE AND RICHARD B. ROBERTS 3 



of cells and then decanting without disturbing the cell pellet. Aliquots of the 

 cells and supernatant fluid were taken for radioactivity measurements. The 

 time elapsed between the immersion of the cells and the decanting of the 

 supernatant fluid was 8 minutes. 



In table i the ratio, radioactivity per ml of cells/radioactivity per ml of 

 medium, is shown to be independent of the sulfate concentration in the medium. 



900 



12 3 4 



Fig. I. Fluid content of E. coli. 



This result demonstrates that a fixed relation exists between the sulfate within 

 the cell and the sulfate of the medium. It is evident that within the 8-minute 

 period of immersion and centrifugation an equilibrium is established across 

 the cell membrane and that in these experiments approximately 72% of the 

 total cell volume is available for the immediate uptake of sulfur. A similar 

 result is obtained when cells are studied in cold saline solution in order to 

 prevent possible metabolic uptake. 



Fluid Content of E. Coli. It can be shown that there is a close correlation 

 between the water space volume of the cells and their actual fluid content. 



