658 ASSOCIATIVE BACTERIAL ACTION 



lacticus, Lactobacillus casei, and Cultures 45.3 and 45.4, two non- 

 lactose-fermenting organisms which have not been identified nor 

 subjected to detailed study. 



The results of a typical experiment are given in Table I. The 

 cultures were grown for 1 month at 30°C. in a medium containing 

 5 per cent lactose, 1 per cent peptone, and an excess of calcium car- 

 bonate. Similar results have been obtained in many different tests 

 and with other organisms. 



From these figures it is seen that this propionic organism is greatly 

 aided in its action by the associated growth of certain other bacteria. 

 In the cases of Streptococcus lacticus and Lactobacillus casei the 



TABLE I. 



Efed of Associative Action. 



Inoculation. 



Propionic organism alone 



" " -\- Streptococcus lacticus . 



" " -[- Lactobacillus casei . . . 



" " -f Culture 45.3 



" " + " 45.4 



Propionic acid 



percent 



0.081 

 0.470 

 0.589 

 0.559 

 0.362 



increased production of propionic acid might be assumed to be due 

 to a greater utilization of the lactic acid produced by these bacteria 

 than of the lactose, since the propionic organism is an active fer- 

 menter of lactates. Von Freudenreich and Jensen' showed that the 

 volatile acids produced from milk by Bacterium acidi propionici (a), 

 a feeble lactose fermenter, could be greatly increased by growing 

 the organism in combination with lactic acid-forming organisms. 

 However, our results obtained in other tests in which the fermentable 

 material consisted of calcium lactate instead of lactose also showed a 

 stimulating effect of Lactobacillus casei upon the propionic acid-pro- 

 ducing organism. In this connection it is interesting to note that 

 certain non-lactose-fermenting bacteria stimulate the propionic acid 

 fermentation of lactose in the same way. 



It is hoped that we may return to this problem at some future 

 time in an effort to throw some Hght on the nature of the associative 

 effect. 



' von Freudenreich, E., and Jensen, O., Landw. Jahrh.,^ 1906, xx, 320. 



