NORMAL AND ABNORMAL MICROFLORA OF MILK 73 



liquefies gelatine and produces an appreciable effect in milk 

 within five hours. Like several allied forms, it may occur in bad 

 water. If a stable once becomes infected with these organisms, 

 nothing short of a very thorough disinfection will eliminate them. 

 The author has isolated a non-liquefying micrococcus, which, being 

 an obligate aerobe, only makes the surface of the milk slimy ; in 

 pure cultures, the sliminess is preserved for many weeks ; the 

 milk becomes faintly alkaline, but is not peptonised. It turns 

 the surface of agar brownish black. Storm has isolated a motile 

 rod which similarly only turns the surface of the milk slimy ; it 

 coagulates and peptonises the milk. As already mentioned, the 

 slime is derived from the outer portion of the cell membrane. 

 While the organisms mentioned can form slime from the protein 

 of the milk, the lactic acid bacteria which produce slime require 

 sugar in order to do so, but, on the other hand, they make the milk 

 slimy throughout. As has been mentioned, the most important 

 slime-producing lactic acid bacteria are certain varieties of 

 Sc. cremoris. 



As far as the Swedish " long milk " or the Dutch " long whey " 

 are concerned, sliminess is a desirable characteristic, but otherwise 

 it is highly undesirable, for slimy cream gives a bad yield of butter, 

 and slimy whey is difficult to press out of cheese, collecting under 

 the rind, and, as Bum has shown, causes the cheese to crack at a 

 later stage 1 . For this reason slimy bacteria are no longer used 

 in making Dutch cheese, as other lactic acid bacteria have been 

 found to possess the same advantages without the disadvantage 

 in question. Further, slimy organisms easily lose their character- 

 istic property, especially if grown at higher temperatures ; con- 

 versely, the common Streptococcus cremoris is inclined to make 

 milk slimy if cultivated at 'lower temperatures for any length of 

 time. Other lactic acid bacteria, pure (certain thermobacteria), 

 as well as pseudo (certain aerogenes bacteria), may cause sliminess. 



Coloured Milk. In the old-fashioned process of allowing milk 

 to stand in order to let the cream rise, coloured spots often 

 appeared on the cream, or the milk would gradually become blue 

 or red throughout. As these defects have not been met with in 

 practice since the introduction of the centrifuge, they need not 

 detain us here. They are due to the colour-producing organisms 

 already mentioned (see pp. 44, 45 and 46). 



Milk with an Unclean Sour Taste. There is no defect more 

 commonly met with in dairies than this one, as it is in no way due 

 to foreign or rare milk organisms. It is simply the stale stage 

 prematurely reached owing to insufficient cooling. 



1 " Centralblatt f. Bakteriologie," 2 Abt., 1904, Bd. XII., p. 192. 



