29 



107 



1% N) obtained diivctly I'roin diiïostion with i)0])sin, partly tin- saim- dilulcd lo Iwico and 

 tour times tiae volume. I'iie solutions were of course neutralised, and ail eonlaiiied tlic 

 same quantity of nutritive salts. 



The table shows distinctly enough that more acid is formed with increasiui^ (luanti- 

 ties of nitrogenous food. When the higiier concentrations of nitrogen are reached, however, 

 the increase does not always amount to anything worth mentioning, and in the case of 

 the betacocci and betabacteria, the highest concentrations even ai)])ear to be detrimental. 

 Despite the buffer action of the nitrogenous food, the quantity of acid cannot increase 

 indefinitely with increasing quantity of nitrogenous nourishment, owing to the fact that, 

 as van Dam has recently shown^), the lactic acid fermentation is not only 

 checked by the hydrogen ions, but also by the lactate ions. It is also a 

 well known fact that only the most powerful lactic acid formers are capable of fermenting 

 all the milk sugar of the milk, even where chalk has been added, and the acid formed has 

 been neutralised by constant shaking. These complications render it impossible to set 

 up any hydrogen ion concentrations as the limit of fermentation for the different species 

 of lactic acid bacteria. The better the buffer action of the nutritive substrate, the more 

 the lactate ions will make their presence felt, and the final concentration of hydrogen ions 

 will be lower in consequence. The lactate ions, however, are not nearly so 

 dangerous to the life of the lactic acid bacteria as the hydrogen ions, 

 and in cultivating lactic acid bacteria, therefore, care should always 

 be taken to employ nutritive substrates With a good buffer action. 



It will be seen from Table IX, that the broth with 0.5% N. in the form of casein pep- 

 ton is a better nutritive substrate for lactic acid bacteria than broth with 0.7% N in the 

 form of Witte peptone, and can in many cases even compare with broth having 1.35% N. 

 in the form of Witte peptone. An das the casein peptone broth is also lighter in colour, 

 than 5% or 10 % Witte peptone broth, and forms no deposit with acid, it will easily be 

 understood that we preferred this for cultivation of lactic acid bacteria, and we use it 

 with just 0.5% JV. as any further increase of the concentration only exceptionally im- 

 proves the action. 



The peculiar behaviour of the aerogenes bacteria towards sugar, to which we have 

 referred in the course of the explanation of Table VIII, is also apparent from Table 

 IX. The quantity of acid rises, it is true, when the quantity of Witte peptone is increased 

 from to 2%, but when this point has been passed, we find that more and more of the 

 acid formed is changed into gas, and as at the same time a certain protein decomposition 



') Ueber den Einfluss der Milclisiiure auf der Milchsiiiiregärung (Biochemische Zeitschrift 1918, 

 Bd. 87, p. 107). In this work, van Dam reproaches me with not having observed the influence of the 

 hydrogen ion concentration upon tlie lactic acid bacteria, basing his accusation upon a brief statement 

 made at a congress with regard to the present work, in which it was quite impossible to enter into 

 any detailed explanation of the individual phenomena. I can, however, console my critic with the 

 fact that Miss .Ienny Hempel - three years before the date of van Dam s paper - had kindly invest- 

 igated, at the Cari.sbekg Laljoratory, the buffer action of the nutritive substrates whicli I was using, 

 and found that it increased in the following order: Witte peptone, casein peptone, and yeast extract. 

 Yeast extract broth witli 0.5 "!„ .\ has about the same buffer action as Witte peptone broth with l.;i5 " .V 

 (i. e. with 10" ,, Witte peptone). 



