BACTERIA IN THE INDUSTRIES 1 85 



inoculates the cheese with pure cultures of the kind of microbe producing 

 the desired flavor as Roquefort, Bre, Limburger, etc. In time it will no 

 doubt be possible to produce hitherto unheard-of cheese flavors by means 

 of new species, varieties, and strains of cheese microbes. Cream- and 

 butter-flavor bacteria are also used. The souring of milk is due to the 

 omnipresent but flly defined Bacillus acidi lactici and other bacteria. 

 Stringy or ropy milk is due to bacterial infection. Under conditions 

 favorable to the development of the organisms, the ropmess appears 

 within from twelve to twenty-four hours after milking, and becomes so 

 pronounced that the milk can be drawn out in long threads or strings. 





Pig. 58. — ^Lactic acid bacillus. There is a large group of bacteria, similar in appear- 

 ance to the lactic acid bacillus, which have the power of forming lactic acid in milk. 

 Some of these are used in pure culture to make the so-called artificial buttermilk. Milk 

 bacteriology is still in its infancy. For so long have we been accustomed to the use of 

 contaminated (filthy) milk that in a recent test made with samples of pure milk and 

 samples of which cow manure was added, 90 per cent, of those who were asked to taste 

 the milks preferred the milk to which the cow manure was added, declaring that it 

 was the only sample which had a "milk flavor." 



It is a not uncommon condition of milk in Switzerland, where is is con- 

 sidered specially noxious, but in Holland it has been produced by design 

 for making Edam cheese. Ropiness of milk is caused by a variety of 

 microorganisms, among them being Bacillus actinobacter, B. lactis vis- 

 cosus, B. gummosus, etc. The microorganism used in Holland for the 

 manufacture of the cheese referred to is known as the Streptococcus Eol- 

 landicus. The Bacillus cyanogenus causes the milk to become blue with- 

 out coagulating it or rendering it acid. The Bacillus butyricus occurs in 

 milk which it coagulates, also producing butyric acid. It is this microbe 

 which develops the rancidity of butter. There aare, however, many dif- 

 ferent species of microbes which produce butyric acid fermentation. 



