4 ELECTROLYTES IK BIOLOGICAL SYSTEMS 



When approximately i gm of wet cells was dried at iio°C and then weighed, 

 the fluid loss in three experiments corresponded to 72, 76, and 74% of the wet 

 weight of the cells. These values are in good agreement with those reported 

 for the fluid content of E. coll by Nicolle and Aliliare (20), and are not sig- 

 nificantly different from the water space volumes reported in tables i and 2. 

 Figure i shows the fluid loss as a function of time when approximately 0.5 gm 

 of wet cells was dried in vacuo. Under these conditions there was a regular 

 loss of water from the cells and in 3 hours 97 % of the water of the cell was 

 removed. The final amount of the fluid removed was 77.7% of the initial 

 weight of the cells. 



Measurement of Water Space by Analysis of the Supernatant Fluid. Another 

 determination of water space may be made by measuring the loss of radio- 



Table 3. Radiosulfate uptake by resting cells measured by analysis 

 OF supernatant fluid* 



* Total radioactivity of 2 ml immersion fluid, 4,208 counts per second. 



activity from the initial immersion fluid. Only two measurements are required: 

 a) the radioactivity of the immersion medium prior to the introduction of 

 the cells, and b) the radioactivity of the cell-free supernatant after centrifuga- 

 tion of the cells. This method of determination has two advantages. When 

 large volumes of cells are employed, no corrections of the radioactivity meas- 

 urements for self-absorption by the cells are necessary. Furthermore, losses 

 due to the rinsing procedures (washing pellet and tube with 0.85% NaCl) 

 are not introduced. 



Table 3 shows the results of a typical experiment. Carrier-free S^^04" was 

 added to 7 ml of S-medium containing glucose and thoroughly mixed. Two ml 

 of this radioactive solution were added to each of three centrifuge tubes con- 

 taining I ml of carrier sulfate solution yielding the final sulfur concentrations 

 shown in table 3. Two 0.5-ml samples of the medium were removed from each 

 tube for radioactivity determination. Each tube was maintained at a different 

 temperature. The contents of each tube were added to one of three new tubes, 

 each containing a pellet of washed cells of a known volume. After resuspension 

 of the cells and immediate centrifugation, the supernatant was decanted and 

 two 0.5-ml samples were removed for radioactivity measurements. Table 3 



