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



cell contents with the normal material of glucose-grown cells 

 would require. Thus the succinic dehydrogenase system 

 continues to be formed in excess of normal requirement for 

 some time. Even when the succinic dehydrogenase has 

 reverted to the level characteristic of growth in the glucose 

 medium the cells have not yet returned to a state where they 

 show a long lag for growth in succinate. This fact reinforces 

 the conclusion that the enhanced succinic dehydrogenase 

 activity is by no means the only factor concerned in the 

 adaptation to the succinate medium. 



The phosphatase activity is characterized by one rather 

 remarkable property, namely rapid increase to pronounced 

 maximum in the early stages of growth, and subsequently 

 rapid decline at a rate which suggests "dilution-out" by the 

 formation of material containing much less of the enzyme. 

 Neither the early rise nor the later fall is due to changes in 

 pH. The initial burst of phosphatase activity seems to occur 

 in direct response to the needs of the young cells at the start 

 of the growth cycle. 



3. Aerobic -Anaerobic Transitions 



One kind of environmental change to which cells are not 

 infrequently exposed and which calls for an appropriate 

 regulation of the metabolism is the transfer from aerobic to 

 anaerobic conditions and vice versa. The behaviour of Bad. 

 lactis aerogenes when confronted with these needs for physio- 

 logical adjustment is typical of cell mechanisms in general, 

 though the behaviour of other bacteria may well differ a good 

 deal in detail. 



Cultures of this organism show a reducing power towards 

 oxygen which can be given a quantitative measure by tests 

 involving the consumption of oxygen and the reduction of 

 methylene blue. Let the measure of this reducing activity be 

 denoted by R. For a wide variety of carbon substrates R 

 attains a constant limiting value, which is the same from 

 substrate to substrate when once the cells have become fully 



