114 MICRO-ORGANISMS AND FERMENTATION. 



Certain Torula yeasts may grow in milk and make it bitter 

 (Calloghan and Harrison). " Ropy " milk has a marked 

 slimy character, and can be drawn out into threads. This is 

 due either to the enormously swollen membrane of certain 

 bacteria, or to the formation of slimy albuminoid bodies. 

 The active micro-organisms are either varieties of lactic acid 

 bacteria, or more particularly the bacteria that digest albumen. 

 A widely distributed species is Bac. lactis viscosus, described 

 by Adametz, which gradually converts the viscid milk into a 

 substance resembling honey. Another widely distributed and 

 active species is Micrococcus Freudenreichii, described by 

 Guillebeau, which liquefies gelatine. The lactic acid bacterium, 

 Streptococcus hollandicus, Hueppe, described by Weigmann, 

 Goethart, Boekhout, and others is of particular interest ; it 

 occurs in Dutch " lange Wei " (a ropy cream used in the 

 manufacture of Edam cheese). This organism is a facultative 

 anaerobe, and has its optimum at 21-22 C. Like many 

 other varieties it easily loses its property of forming slime. 

 A similar variety was found by G. Troili-Petersson in the 

 Swedish " tatmjolk " (thick milk), and described under the 

 name of Bact. lactis longi. It is believed that this species con- 

 structs slime from lactose. It has its optimum below 20 C. 

 Probably such bacteria are present on certain plants that are 

 placed in the milk, such as Pinguicula and Drosera. 



By the action of micro-organisms milk may assume a blue, 

 red, or yellow colour. The blue coloration of milk depends 

 upon the growth of certain species of bacteria, the presence 

 of which was proved by Fuchs as early as 1841. Hueppe 

 was the first to prepare a pure culture of one of these species, 

 and he described it under the name Bacillus cyanogenus (Bact. 

 syncyaneurri), which occurs as a short motile rod. In the 

 case of this, the most widely distributed species, the colour 

 appears first on the surface of the raw milk, and afterwards 

 penetrates to the lower layers. The production of colouring 

 matter originates from the albuminoids, and may occur in 

 the absence of sugar. A number of the water bacteria also 

 have the power of imparting a blue colour to milk. The 

 reddish colour which milk occasionally assumes is also due 

 in certain cases to bacteria. Only a few examples are quoted in 



