318 A. C. R. Dean and Sir Cyril Hinshelwood 



metabolism. No enzyme adjustments appear to be necessary, 

 the cells having apparently retained unimpaired their ability 

 to utilize molecular oxygen when it becomes available (Baskett 

 and Hinshelwood, 1951a). 



The increased consumption of carbon source in anaerobic 

 growth, and the increased economy of utilization in presence 

 of oxygen is, of course, an example of the well known Pasteur 

 effect. The part of this phenomenon which at first sight 

 presents an almost purposeful air is the inhibition of the 

 wasteful substrate consumption as soon as oxygen is provided 

 to give a more efficient mode of utilization. The mechanism is, 

 however, purely automatic, depending essentially on the fact 

 that oxygen immediately lowers the ratio of the reduced to 

 the oxidized carriers in the system and thereby largely cuts 

 out the competing reactions into which the former might have 

 entered. The saving of substrate depends upon the simple 

 chemical fact that whereas a carbon compound can be 

 oxidized fairly readily to carbon dioxide and water, it can only 

 act as a hydrogen acceptor in the fermentative type of reaction 

 relatively inefficiently since the formation of fully reduced 

 products such as paraffins is structurally seldom possible 

 (Baskett and Hinshelwood, 19516). 



4. Alkali Metal Ions and pH Regulation 



The passage of alkali metal ions into or out of the cell 

 plays a major part in regulating carbohydrate metabolism. It 

 also plays some part, in our view an indirect one, in the 

 response of the cell to adverse pH changes, a phenomenon in 

 which other factors are also important. The more general 

 aspect of alkali metal ion metabolism will therefore be 

 considered first (Eddy and Hinshelwood, 1951; Eddy et al., 

 1951). 



With Bad. lactis aerogenes K+ or Rb+ ions are necessary for 

 growth, and cannot be replaced by other members of the 

 alkali metal series (Eddy and Hinshelwood, 1950). Smaller 

 as well as larger ions are ineffectual, so that a specifically 



