vi] THE BACTERIA OF MILK 95 



sugar with such energy that gaseous products are 

 evolved, and the cheese becomes perforated with holes. 

 To one such class of bacteria Freudenreich has 

 applied the name Schaffer bacillus. It seems to be 

 closely related to a bacterium common in the intestine 

 bacterium coli commune. It is hence of the greatest 

 importance that milk should not become contamin- 

 ated, in the process of milking, with cow-dung. 



Butyric Fermentation. Occasionally it happens 

 that milk or cream coagulates without any previous 

 lactic fermentation. This is seen in the coagulation 

 of milk which has been boiled, and the reaction of 

 which is neutral. In this type of fermentation, 

 which is accompanied by the development of an 

 alkaline reaction, and not an acid reaction, the 

 changes are similar to those effected by rennet. It 

 is characterised by the formation of a bitter taste, 

 and by the solution of the coagulum into a somewhat 

 clear liquid, and the formation of butyric acid. It is 

 caused chiefly by the butyric bacillus, but here again 

 we seem to have a number of different bacteria 

 working. Indeed it would seem that there are quite 

 a number of bacteria producing butyric acid.* It 

 has been suggested, therefore, to constitute a group 

 of butyric ferments. If, however, as Freudenreich 

 truly points out, 1 butyric acid is rather to be regarded 

 as a residue resulting from the breaking down of 

 1 See Dairy Bacteriology, p. 88. 



