Automatic Adjustment in Bacterial Cells 319 



correct ionic radius is evidently more important than mere 

 permeability, a conclusion borne out by the work of Roberts 

 and his colleagues (Roberts, Roberts and Cowie, 1949; Cowie, 

 Roberts and Roberts, 1949; Roberts and Roberts, 1950). 



During metabolism a positive stream of alkali cations 

 enters the cell together with the negative stream of phosphate 

 ions. The alkali cations appear to become incorporated in 

 some structure involving an enzyme surface where phos- 

 phorylated intermediates of the carbohydrate metabolism are 

 dealt with. This specific structure appears important in 

 explaining the size specificity, and its stability can be invoked 

 to explain the action of the alkali ions in displacing hydrions. 

 In this sense the potassium or rubidium ions protect the cell 

 against an adverse pH. If the hydrion concentration of the 

 cell rises, enzyme reactions by which phosphate is incorpor- 

 ated into the cells are slowed down. The alkali ion which 

 would normally be released to deal with more phosphate 

 remains bound and the total amount of K+ or Rb+ in the cell 

 rises. Observations with radioactive tracers show that when 

 the pH of cells actively metabolizing glucose is lowered there 

 is a temporary displacement of alkali ion, due to the direct 

 competition of hydrion, followed by an increase in the maxi- 

 mum uptake as the internal adjustments are completed. 

 When the carbohydrate metabolism ceases the alkali metal 

 ions leave the cell. From resting cells, decrease in pH facilitates 

 this displacement. The alkali ion is not an essential structural 

 component of the cell, at any rate in considerable amounts, 

 but is an enzyme activator and metabolic regulator. 



If dehydrogenase activity is adversely affected by increasing 

 acidity, addition of potassium ions lessens the fall, an antagon- 

 istic action not in evidence with deaminase activity. 



The influence of pH on the growth rate of the cells is 

 interesting. Over a wide range, pH 7 to 5, the actual value of 

 the initial generation time is unchanged, though the total 

 population which the medium can support falls steeply as the 

 acidity increases (Lodge and Hinshelwood, 1939). If the pH 

 of a dividing culture is suddenly dropped by about • 7 unit 



