MILK FERMENTATIONS 79 



In order to determine whether the various types of colonies 

 appearing on the plates are able to ferment lactose, tubes of 

 sterile milk or whey are inoculated, incubated at 20 C. and 

 at 37 C. The production of gas (C0 2 ), which becomes evi- 

 dent on shaking the tube slightly, is evidence of the fermen- 

 tation of the lactose. Few of the yeasts produce any curdling 

 of the milk. The presence of alcohol is usually made evident 

 by the odor. The iodoform test for alcohol should be made 

 by distilling over a small quantity from a mass culture in 

 milk or whey, made alkaline with milk of lime. Add to 5 cc. 

 of the distillate three or four drops of a 10 per cent solution of 

 iodine in potassium iodide, until a permanent reddish-brown 

 color is obtained. Decolorize by adding 10 per cent KOH 

 drop by drop. Allow the tube to stand in warm water until 

 a sediment collects. Examine with the -inch lens for the 

 characteristic crystals of iodoform. The method should first 

 be tried with distilled water to which a few drops of alcohol 

 have been added. 



Ropy fermentation. The peculiar change in milk, known 

 as ropy, slimy, or stringy milk, may be produced by a large 

 number of forms of bacteria. With many it is apparently a 

 normal property, with others it is an evidence of degeneration 

 changes. Some types of lactic-acid bacteria, on cultivation, 

 cease to curdle the milk in a normal manner, but produce 

 in it varying amounts of a slimy material. ' 



The upper layers of cream and milk in bottles may become 

 slimy, due to the growth of aerobic organisms (B. mesenteri- 

 cns vulgatus). The slime-producing organisms proper may 

 or may not produce acid. The organisms studied by Ward, 

 Harrison, etc., belong to the latter group (B. lactis viscosus). 

 The bacteria present in the slimy whey (lange wei) of 

 Holland (Streptococcus ffollandicus), in the taettemoelk of 



