ADAPTIVE AND CONSTITUTIVE ENZYMES 91 



According to Karstrom the formation of adaptive 

 enzymes is always associated wnth the life processes of 

 the cells. Dead cells can never give rise to enzymes 

 which were not present in the living cells. If adaptive 

 enz\Tnes appear in a culture which exhibits no gro^^i:h 

 (for instance, where the growth has been prevented by 

 some particular treatment, as is the case with the 

 " resting " bacteria of Quastel and his co-workers) it 

 must be assumed that such cells, although incapa})le of 

 cell division in the given circumstances, are not dead ])ut 

 in a state of suspended animation. 



We will describe some of Karstrom's experiments with 

 Aerohacfer aerogenes (B. aerogenes) which he grew on a 

 lactose medium. He separated the cells by centrifugalisa- 

 tion, washed them and suspended them in solutions 

 containing xylose and calcium carbonate (the latter to 

 prevent development of acidity). Four solutions were 

 used containing, besides the cells, xylose and calcium 

 carbonate : — 



1. Sodium chloride. 



2. Potassium phosphate. 



3. Potassium phosphate and yeast water. 



4. Potassium phosphate and ammonium sulphate. 

 The fermentation of xylose by the cells in these solutions 

 was measured by the amount of carbon dioxide evolved, 

 with the results show^n in Table 5. 



Table 5 



