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DAIRY BACTERIOLOGY 



of many years 1 have established that the Tyrothrix bacteria are 

 comparatively rare in cheese, that normally they cannot develop 

 in cheese even if introduced in large numbers, owing to their 

 sensitiveness to acid, and finally that if conditions favourable 

 to their growth are secured by using pasteurised milk and emitting 

 the addition of lactic acid bacteria, they produce a disgusting 

 taste of putrefaction in the cheese. The bacteria living in the 



interior portions of the cheese are nearly exclusively of the 

 lactic acid group, and it must consequently be these which are 

 principally responsible for the protein hydrolysis which takes 

 place. Freudenreich, who devoted special attention to Emmental 

 cheese, found chiefly the rod-shaped species, and succeeded in 

 showing that these were able to attack casein if only the lactic 

 acid which they produced was neutralised by chalk as completely 

 as it is neutralised in the hard cheese. This forms the basis of a 



1 The first of Freudenreich' s papers on this subject appeared in " Annales 

 de Micrographie," 1889, p. 257, while the subsequent ones are nearly all 

 published in " Landwirtschaftliches Jahrbuch der Schweiz," 1891 to 1906. 



