96 BACTERIOLOGICAL CHEMISTRY 



logarithmic phase of growth all the enzymes may be of 

 approximately equal intensity. Undoubtedly, though, in 

 many cases a real stimulation of enzymes does occur 

 under the influence of the specific substrates. The 

 production of enzymes by bacteria is also influenced 

 by substances other than the specific substrate. Thus 

 calcium is necessary for the formation of gelatinase by 

 Proteus vulgaris and magnesium for the phosphatases of 

 propionic acid bacteria. The presence or absence of 

 growth substances in the medium and the pH. of the 

 medium are factors which must be taken into account 

 when considering enzyme synthesis. 



Some adaptive enzymes are more easily produced than 

 others. Karstrom showed that Esch. coli, for instance, 

 produced enzymes to deal with mannitol in seventy- 

 five minutes, sucrose in 105 minutes and lactose in 165 

 minutes. The production of the necessary enzymes in 

 training " exacting " strains is usually much slower. 



The production of the galactose fermenting enzyme 

 by yeast is a true adaptation, since it has also been shown 

 to occur in the absence of cell division, which rules out 

 the selection hypothesis. On the other hand, the pro- 

 duction of lactose fermenting variants by Esch. coli 

 mutabile seems to be a true selection, since it has been 

 shown that such variants are being continuously produced 

 even in the absence of lactose. In this case the effect of 

 lactose in the medium is to provide the most favourable 

 conditions for the growth and identification of the 

 mutants. 



The majority of constitutive enzymes are those which 

 bring about the respiratory and sjmthetic processes of 

 the bacteria, whilst most of the adaptive enzymes are 

 to be found among the hydrolases which break down the 

 more complex nutrient materials to a form suitable for 

 the attack of the constitutive enzymes. Exceptions to 

 this rule are the production of the enzymes which enable 

 " exacting " organisms to become " non-exacting " and 



