196 BACTERIA IN BUTTER. 



ripened cream which produced a high-grade butter. There is 

 no difficulty in obtaining from such cream the kinds of bac- 

 teria that are present in the greatest abundance. For reasons 

 already pointed out, the organisms that have been obtained 

 in this way and used for this purpose have been, in practic- 

 ally all cases, lactic organisms, since they are by far the most 

 abundant in well-ripened cream. Consequently, lactic organ- 

 isms have been practically always selected as the types of 

 pure cultures to be used for cream ripening. But it is almost 

 certain that the chemical changes occurring in normal cream 

 ripening are not produced by the growth of any one bac- 

 terium. It is not to be expected, therefore, that any one 

 species of bacterium can be found which would produce 

 normal ripening with the typical results. Consequently some 

 of the cultures which have been used have been mixtures 

 of different species of bacteria, obtained according to the 

 idea that such mixtures would be more liable to produce 

 normal results than any single pure culture. Mixtures that 

 have been hitherto used, however, have been purely accidental 

 ones consisting in most cases of such mixtures as would be 

 found by simply drying a mass of ripening cream. Thus far, 

 no practical attempts have been made to prepare artificial 

 mixtures of species for the purpose of giving a normal 

 ripening. 



Quite a number of such commercial cultures are upon 

 the market to-day. They are for sale in the chief butter- 

 making countries by dealers in dairy supplies. They go by 

 various names, sometimes by the name of the person who 

 makes them, and again by some commercial name. They 

 differ from each other more or less, and the results obtained 

 by the use of them are slightly variable. In general, how- 

 ever, they are cultures of one species of lactic bacterium, 

 pure cultures, though some are mixtures. 



It must be noticed, further, that the problem of a proper 

 culture for cream ripening will be different in different 



