782 BACTERIA: THEIR WORK 



play an important part in the 'ripening' process to which 

 cream is subjected in this country before being churned. The 

 development of a small amount of lactic acid in the cream 

 increases the yield of butter which can be practically obtained 

 from it by churning, and doubtless influences the flavour of the 

 butter also. 



In order to secure the presence of the lactic organisms upon 

 which the required degree of acidity depends, it is generally 

 customary to add to the ' sweet ' cream a small quantity of sour 

 milk, buttermilk from a previous churning, or a pure-culture of 

 the lactic bacteria. 



Besides milk-sugar, other sugars such as maltose, cane-sugar, 

 and glucose, are transformed partially into lactic acid by various 

 species of bacteria, and the development of sourness in beer, 

 wine and other liquids is sometimes due to the formation of this 

 acid from the soluble carbohydrates present. 



4. Butyric Fermentations. — Fermentations which result in the 

 production of butyric acid are common, and a considerable 

 number of bacteria capable of inducing the formation of this 

 acid in various media have been studied by different workers. 

 Much of the investigation has been of a disconnected and 

 untrustworthy character, and the relationships and powers of 

 the various species or forms of the organisms dealt with by 

 the many workers in this field of research is still somewhat 

 uncertain. 



From the recent investigations of Schattenfroh and Grass- 

 berger it would appear that the various forms described by 

 Prazmowski, Gruber, Beyerinck, Klecki, and others, may be 

 reduced to two chief species or races belonging to the genus 

 Granulobacillus. 



One species is non-motile, the other motile: the non-motile 

 forms liquefy gelatine, while the motile ones do not. 



Both species and their forms are common in milk and 



