TREATMENT OF CREAM PREVIOUS TO THE CHURNING. 209 



cream is inoculated into sterilized milk, certain ones will 

 soon gain superiority and produce their specific fermenta- 

 tion. If some of the soured sample taken when the fer- 

 mentation is most active is then inoculated into a new lot 

 of sterilized milk and the inoculation repeated in the same 

 way, cultures of a certain bacteria are after awhile obtained 

 which in most cases may be considered pure. The sub- 

 stratum has then offered so favorable conditions of life to 

 this kind of bacteria that it has been able to suppress all 

 others. In this manner I once obtained a pure culture 

 of a lactic-acid bacteria from a very impure sample of 

 milk.* 



How do these conditions occcur in practice in the 

 ripening cream in shallow pans ? In the first place the 

 lactic-acid bacteria are favored in every way in these, milk 

 being the most favorable nutritive medium imaginable. 

 Secondly, souring material is transferred partly uncon- 

 sciously (the wall and bottom of the pan), partly con- 

 sciously by addition of sour milk in which the fermentation 

 is at its height. It will be seen that there are here many 

 points of similarity with the method applied in laboratories 

 for production of pure cultures. Conscious infection by 

 means of sour milk does not often take place in farm- 

 dairying, and is only resorted to when the unconscious 

 infection has proved insufficient. I have, however, found 

 places in Savolaks where such inoculation of acid bacteria 

 has been the rule and was applied almost daily. This in- 

 fection in one place occurred by dipping the wooden spoon 

 used in skimming the sour-milk pans into the pan con- 



* " Studien tiber die Zersetzungen der Milch," in Fortschritie der 

 Medicin, 1889, pp. 122, 123. 



