BACTERIA. 73 



lactic acid bacteria occurring in mash. It is not yet known 

 whether one single species always predominates or whether 

 several species are active in spontaneous acidification. 



Since the year 1890 methodically selected species of bacteria 

 have been made use of in a similar way in dairies for the 

 purpose of bringing about a regular and certain acidification of 

 the cream used in the manufacture of butter. The progress 

 made in this field is associated with the researches of STORCH, 

 WEIGMANN, QUIST, and others. The pure culture selected is 

 added to skim-milk previously heated to 60-70C., and the 

 culture is allowed to develop at about 15 C. After standing 

 24 hours, this mass-culture is fit for use. In order to render 

 the cream which is to receive the culture as free from germs 

 as circumstances permit, it is first cooled down to a low 

 temperature, and then quickly warmed up to about 20 C., 

 or else it is pasteurised. For a period of 24 hours the 

 mass-culture is allowed to develop in cream before churning is 

 commenced. 



Among the forms isolated by STORCH (Copenhagen, 1890) 

 from butter, acidulated cream, and butter- milk, the Coccus 



FIG. 20 a. Lactic acid bacteria. (After STORCH.) 



form seems, according to WEIGMANN, to be the most frequent 

 species and the one best suited to the acidification of the cream. 

 It occurs in a large number of varieties, which, according to 

 their main characteristics, may be distributed into two groups: 



