Automatic Adjustment in Bacterial Cells 317 



adapted to aerobic growth on the one in use. The different 

 carbon sources, however, support growth at very different 

 rates, from which it may be inferred that the growth of the 

 fully adapted culture is limited in rate by a part of the cell 

 mechanism which consumes molecular oxygen. When the 

 cells are first offered one of these substrates, however, growth 

 is much slower than the optimum and R is correspondingly 

 less than the maximum value. As adaptation to the new 

 source proceeds R and the growth rate increase in a parallel 

 manner to their respective optima. It seems, therefore, that 

 until the enzyme proportions have settled down to equilibrium 

 values the substrate itself can not be metabolized up to the 

 limit permitted by the mechanisms consuming molecular 

 oxygen. During aerobic growth in a new carbon substrate, 

 then, the first adjustment is a slow establishment of enzyme 

 ratios allowing the full utilization of the oxygen supply 

 (Baskett and Hinshelwood, 1950). 



If an adapted aerobic culture is made anaerobic while in 

 active growth, multiplication is at once arrested and the value 

 of R rises. After a considerable but variable delay growth is 

 resumed at the lower rate corresponding to the anaerobic 

 conditions, R drops more or less to its original value and the 

 consumption of the carbon source for each unit of bacterial 

 mass produced becomes much larger. These adjustments do 

 not occur in the absence of a nitrogen source. It appears that 

 the resumption of growth in the anaerobic conditions demands 

 the synthesis of new enzyme facilities, permitting the reoxida- 

 tion of reduced carriers no longer by molecular oxygen but, 

 directly or indirectly, by the carbon substrate. Until these 

 new facilities have been developed by adaptive adjustments, 

 reduced carriers accumulate in the cell and may account for 

 the enhanced value of R observed during the arrest period. 



When, on the other hand, a culture growing anaerobically 

 is suddenly provided with aeration the response is almost 

 immediate and the growth rate rises without any period of 

 delay to the higher value. The consumption of the carbon 

 substrate rapidly falls to that characteristic of aerobic 



