1211 



for then 







or, aecordittg to the expansion II 



1 r -- 



ƒ (t/) = — I cos ^ ?f g -^ (^" + ^ ' ") ^"i 

 2jr J 







which reduced by b Art. 6, gives 





Microbiology. — ^'On the nitrate ferment and the formation oj 

 physiological species'. By Prof. Dr. M. W. Beijerimck. 



(Communicated in the meeting of March 28, 1913). 



It is a well-known fact that in soil as well as in liquids containing 

 a great many individuals of the nitrate ferment, large amounts of 

 organic substances may be present without preventing nitratation, 

 whicli is the oxidation of nitrites to nitrates by that ferment. 



On the other hand it is certain, that when only few germs of the 

 ferment are present, so that they must first grow and multiply in 

 order to exert a perceptible influence, extremely small quantities of 

 organic substance are already suflicient to make the experiments fail 

 altogether, the nitrite then remaining unchanged in the culture media. 



It is generally supposed, that this latter circumstance must be 

 expUxined by accepting tliat the nitrate ferment can only then grow 

 and increase, when soluble organic substances are nearly or wholly 

 absent. 



My own experiments, however, have led me to quite another 

 result, namely that the nitrate ferment very easily grows and increases 

 in presence of the most various organic substances. But in this case, 

 that is, luhen growing at the expense of organic food, it soon wholly 

 loses the power of oxidising nitrites to nitrates and then changes 

 into an apparently common saprophytic bacterium. 



This change may be called the formation of a physiological 

 species, and the two conditions of the ferment thus resulting, respec- 

 tively the oligotrophic and the polytrophic form. 



