2QO 



not, however, rise above 10 12 c.c. normal in 100 c.c. of milk. On whey agar 

 or whey gelatin plates the growth at the air of the thus obtained lactococci is 

 different, as sometimes a great many aerobic colonies arise, which cause the same 

 acidification as the cultures in the bottles, while in other cases nothing is seen 

 to grow. 



The first group corresponds with the usual commercial forms destined for 

 the souring of cream, which commonly consist of cultures of the microbes dried 

 on milk sugar or starch; moreover there are commercial aerobic pure cultures 

 in milk or whey, which are sold in bottles. 



The second group, that is the cultures non-growing at the air, may still 

 better be used for the cream souring than the aerobic stocks, as the anaerobic 

 forms of Lactococcus show more aptness to secrete the flavour desired in butter, 

 than the more aerophilous bacteria 1 ). 



As well for this reason as for the great purity of the cultures made after 

 this bottle method, there is reason to prefer them in dairy work to the com- 

 mercial so-called pure cultures, which for the greater part are by no means pure, 

 but mostly contain, besides lactococci, numerous contamination germs of the 

 milk. In consequence of frequent investigations I can therefore advise insterested 

 persons to use the here described method. Best would be if these cultures were 

 prepared in the creameries themselves, but also the sellers of pure cultures, by 

 following the above prescriptions, will obtain a better product than by the more 

 usual way of selection of aerobic colonies. Besides, the management is simpler 

 and more scientific. 



To my opinion there is no satisfying ground to class the aerobic and an- 

 aerobic forms of Lactococcus, which can be produced after the said method, in 

 separate species. They are but variants of one and the same species, whose 

 oxygen requirements are different, which also appears from the fact that in the 

 course of time one and the same stock shows considerable differences with re- 

 gard to the said relation. Moreover, by several isolations all transitions between 

 the more or less aerobic stocks may be obtained. 



Finally it should be borne in mind, that by applying the bottle method 

 at low temperature, in rare cases instead of a culture of real Lactococcus a Lacto- 

 bacillus is obtained, which may likewise be. had by colony selection from cheese. 

 Using this Lactobadllus I did not observe at all the pleasant flavour of the an- 

 aerobic lactococci, so that I do not recommend these bacilli for cream souring. 



5. Elective culture of the lactic acid bacilli. 



If milk, soured spontaneously by Lactococcus lactis, or still better, buttermilk, 

 is placed at exclusion of air in a thermostat of ca. 40 C, the original acid 

 amount of 8 to 12 c.c. will in most cases rise after some days to about 18 or 

 20 c.c. per 100 c.c. of milk. For this experiment it is best to use a stoppered 

 bottle of 250 to 300 c.c. capacity quite filled with milk. If for the first experiment 



have also met with such like anaerobic lactic acid bacteria in com- 

 mercial preparations. 



