i6 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



of washed T. titilis from the same culture were suspended in the medium. 

 After immersion the cells were immediately centrifuged and samples of the 

 supernatant fluid were kept for radioactivity measurements. The pellet was 

 washed twice with saline solution, and aliquots of the washed cells and washes 

 were removed. The distribution of radioactivity found in these samples is 

 shown in table 12. 



The data of this table show that the azide was eflfective in reducing the 

 quantity of bound phosphate from 11 to 4. The quantity of radioactivity found 

 in the washing solutions (the unbound water space content of the cells), how- 

 ever, was not changed by the presence of the azide. The water space determined 

 by subtracting the residual bound phosphate from the total radioactivity of 

 the cells was 72% and 74%. Consequently, the azide does not appear to have 

 any effect on the ability of phosphate to penetrate the cell wall. 



Table 12. Radiophosphate uptake by t. utilis 



One-dimensional chromatograms were made to demonstrate that the radio- 

 activity removed by the wash solution was radiophosphate. Identical chromato- 

 graphic results were observed for all washes and for a control run of the original 

 medium before the immersion of the cells. No metabolic products were detected 

 on the chromatograms. 



When these cells were dried at iio°C for six hours, the loss of water corre- 

 sponded to 76.9% of their wet weight. Other determinations on different cul- 

 tures gave values of the fluid content ranging from 68 to 77%. All determina- 

 tions were made on cells in the stationary growth phase. 



The calculations of water space obtained from the data of table 12 are based 

 on the radioactivity taken up per gram wet weight of cells. The agreement 

 between the fluid-content and water-space values is obvious. 



The measured water space cannot be due to trapped fluid in the interstices 

 of the packed pellet of cells. According to Conway and Downey (7) the theo- 

 retical interspace for a large number of nondeformable spheres with closest 

 packing is 26%. These authors showed that centrifuged yeast (3,000 revolu- 



