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vigorous. We Ihen sec that after 2 or 3 days the milk beconiö 

 slimy and by inoculation into milk whey, a culture will start which 

 sometimes differs so little from the ordinary Ion»- whey, thai we 

 may conclude lo an identity of species. 



Of course, I cannot foretell thai such microbes occur in any yeast 

 sample taken at random, hence I must add thai for my experiments 

 I used pressed yeast from the Yeast and Alcohol manufactory at Delft. 



Such a culture in milk differs il is true in some respects from 

 what is obtained by growing long whey from North Holland in milk, 

 as in the former case short rods or oblong cocci are observed, and 

 in the latter, shorter forms more reminding of the common micrococci. 



I expecl 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 t/i<> 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" ('. or lower, and as all species 

 of Lactococcus (like those of Lactobacillus) are strongly microaero- 

 philous, 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 tilled with commercial milk and placed 

 at 30 C. After 24 hours or somewhat later a Lact0C0CCUS-üor& 

 begins to replace the other microbes, while not seldom a feeble 

 fermentation of II. coll or A', aërogenes has preceded. 



After one or two re-inoculations under tlie same conditions, but 



'•) It is not impossible that there are "peptones" which, together with glucose 

 or lactose, are still better food lor the lactic acid ferments than milk itself. H<>\\ 

 very differently peptones of dissimilar origin acl on microbes is easily observed in 

 yeast species which in general grow heller on "plant peptones" than on "animal 

 peptones". The introduction of the wool "bios" to denote those nitrogen compounds 

 which are best lit as yeast food, is an attempt to circumscribe the peptoneproblem 

 1m- been given. The relation between "peptones" ami the lactic acid ferments is 

 still closer than between these substances and the different yeasts; hut it is here 

 not the place lo insist <m this point. 



