28g 



case short rods or oblong cocci are observed, and in the latter, shorter forms 

 more reminding of the common micrococci. 



I expect that by repeating this experiment various deviating varieties will 

 be found, and by application of the method to other infection material perhaps 

 new species of slime lactic acid ferments may be discovered. 



4. Elective culture of the lactococci of cream souring. 



As the lactococci and lactobacilli, which both occur in spontaneously or 

 otherwise soured milk, in cheese, and various other dairy products, seem to grow 

 nowhere better than in milk, 1 ) the culture experiments here considered, should 

 be taken with milk. 



In order out of the innumerable microbes of the crude milk practically to 

 come to a pure culture of Lactococcus, the management is as follows. 



The optimum of growth is at 30 C. or lower, and as all species of Lacto- 

 coccus (like those of Lactobacillus) are strongly microaerophilous, sometimes even 

 anaerobic (i. e. cannot grow at all at full atmospheric pressure on plates), it is 

 best to cultivate in absence of air. 



A stoppered bottle is quite filled with commercial milk and placed at 30 C. 

 After 24 hours or somewhat later a Laetococcus-ftovz begins to replace the other 

 microbes, while not seldom a feeble fermentation of B. coli or B. acrogenes has 

 preceded. 



After one or two re-inoculations under the same conditions, but into well 

 boiled milk, which is done by transferring a trace of the first culture to the 

 second bottle, quite filled with boiled, air-free milk, and so on, the lactococci 

 free themselves completely from all foreign microbes and a material is obtained, 

 which displays a high degree of purity and of practical usefulness. If the acidi- 

 fying power of the microbes obtained by the experiment is lower than wished 

 for, for example 5, whilst 8 to 10 c.c. of normal acid on 100 c.c. milk is desired, 

 this must be attributed to the accidentally present stock. It is necessary then 

 to begin a new experiment, following the same way as described, or it can be 

 advisable to perform the first inoculation with some good butter-milk. 



As buttermilk, however, very often contains lactose yeast, in the latter case 

 a vigorous alcohol fermentation may at first be expected in the bottles. But it 

 soon disappears by inoculation into milk rendered free from oxygen by boiling. 



If in this way, thus in absence of air, the culture has been prolonged, a 

 fairly constant acid amount is obtained at each renewed inoculation, which does 



*) It is not impossible that there are peptones which, together with glucose or 

 lactose, are still better food for the lactic acid ferments than milk itself. How very 

 differently peptones of dissimilar origin act on microbes is easily observed in yeast 

 species which in general grow better on plant peptones than on animal peptones*. 

 The introduction of the word bios to denote those nitrogen compounds which are 

 best fit as yeast food, is an attempt to circumscribe the peptoneproblem has been 

 given. The relation between peptones and the lactic acid ferments is still closer than 

 between these substances and the different yeasts; but it is here not the place to in- 

 sist on this point. 



M. W. Beijerinck, Verzamelde Geschriften ; Vierde Deel. 19 



