244 AGRICULTURAL BACTERIOLOGY. 



greater vigor that they overcame the miscellaneous bacteria 

 which were there at the outset. A natural starter is thus not 

 a pure culture, but is made up commonly of over 95 per cent, 

 of tivo or three species or varieties of common lactic bacteria. 



If we compare the results obtained by the use of com- 

 mercial cultures and those obtained by natural starters in 

 general dairying, we find little to choose between them. Both 

 methods are useful, and in many cases there has been a general 

 improvement in the quality of the butter obtained. As a 

 result of experimental tests in some cases the natural starter 

 has produced the best results, and in others the commercial 

 starters. But, so far as present experience of dairymen has 

 gone, there is nothing special to choose between the two 

 methods of preparing a starter. It may be possible that, in 

 time, bacteriologists will be able to prepare a starter which 

 is superior to a natural starter, but up to the present they have 

 not succeeded. 



Hence, the method which. a butter-maker will adopt of 

 obtaining a starter will be dependent upon convenience and 

 local conditions. It may frequently be more convenient for 

 him to purchase a commercial culture than to hunt up a proper 

 dairy and obtain the proper milk for a good natural starter. 

 Moreover, the starter made from a commercial culture may be 

 relied upon as being practically constant, while this is not 

 true of the natural starter. On the other hand, the commercial 

 culture is a matter of some little expense, although it has been 

 greatly reduced in recent years. For this reason the greater 

 number of butter-makers in this country prefer making their 

 own starters to purchasing commercial cultures. 



VALUE OF PURE CULTURES. 



As to the general value of the application of pure cultures 

 to butter-making, the following conclusions may fairly repre- 

 sent the case : The application of pure cultures has taught 



