The Enzymes o/B. coli communis. 141 



Tapidly in doing so, but some of the individuals adapt themselves to the 

 ■anaerobic conditions and probably this means that they possess a mechanism 

 for using combined oxygen. This is discussed later. The results described in 

 this communication must be considered in the light of these remarks for 

 ■doubtless the increase of lactic acid following admission of oxygen in 

 Experiment I is to be referred to an increased vitality of the bacterial culture, 

 i.e., either the bacteria increased in numbers, or they took longer to die. On 

 the other hand it may be that oxygen is necessary under certain circumstances 

 for the action of the enzyme mechanism which produces lactic acid, but this 

 seems unlikely for reasons stated in the discussion later. 



Discussion of Results. 



B. coli communis grows better in air than in an atmosphere of hydrogen 

 :and ferments glucose more vigorously anaerobically after growth in aii- than 

 after anaerobic growth. The type of fermentation differs according as the 

 immediate past history of the organism has been aerobic or anaerobic. In 

 the latter case, no lactic acid or only a very slight yield is obtained, and also 

 succinic acid tends to be absent. 



The manner in which oxygen affects the fermenting powers of the bacteria 

 ^subsequently is not obvious, but it seems likely that the oxygen has acted as a 

 stimulus to reproduction, so that when subsequently fermentation takes place 

 multiplication of cells occurs, whereas when this stimulus is absent, as iu the 

 anaerobic past history, the fermentation occurs without such reproduction. 

 This view accords well with the observations recorded in Part III of this 

 series where only during a period of cell multiplication was lactic acid 

 produced. 



Oxygen in the free state is not necessary for lactic acid production if the 

 bacteria are allowed to. multiply in a nitrogenous medium such as peptone, 

 but in the case of bacteria grown previously anaerobically on agar the 

 stimulus of oxygen seems necessary for the production of lactic acid. It is 

 probable that the oxygen acts by increasing cell multiplication, but this has 

 not been proved. 



Summing up then, lactic acid production is associated with rapid multipli- 

 ■cation of cells, and the cause of lactic acid increase when oxygen is admitted 

 is probably due to stimulation of growth. 



Death of the cells and conditions of depressed vitality are associated with 

 the production of carbon dioxide and acetic acid or alcohol. 



These results may possibly explain the phenomenon of increased growth of 

 yeast due to preliminary aeration. Horace Brown put forward as an 

 •explanation the idea that oxygen was stored up, and subsequent reproduction 



