CHANGES IN MILK 55 



causes the cultures to stink (butyric acid fermentation). 

 Finally, the milk is changed into a watery mixture 

 which contains some fat lumps and has a more or less 

 disagreeable odor. 



e. Bacteria cause coagulation of milk, partly by the 

 production of acid and partly by the action of ferments. 

 Many bacteria as, for example, certain lactic acid 

 bacteria and some members of the colon group, coagulate 

 milk through the production of acid. The precipitated 

 casein is, however, insoluble in diluted lime water, which 

 is an indication that it has been changed, by the action of 

 ferments, into paracasein. 



/. Bacteria may produce a slimy condition in milk or 

 in cream. In this condition, these fluids become thick 

 and their consistency is so great that long strings may 

 be drawn out. The milk may, at the same time, become 

 acid, although usually this is not the case. There are 

 many bacteria of different kinds that are capable of 

 causing this change. In some cases, the sticky condition 

 comes from the rapid swelling of the slimy capsules of 

 the bacteria, while in other cases the change is thought 

 to be due to unidentified changes in some constituents of 

 the milk, presumably the lactose. It has been thought 

 that this slimy condition may be caused by feeding a 

 certain plant, Pinguicula vulgaris, in the same manner 

 that placing the leaves of this plant in milk may produce 

 the change. 



Jonsson has found that there are bacteria on the 

 leaves of this plant that make milk slimy or stringy, 

 therefore it is, no doubt, safe to conclude that feeding 

 with this plant is without special significance in this 

 particular. Stringy milk is not unwholesome ; in north- 

 ern Sweden it is eaten in the same manner as coagulated 

 milk is used elsewhere. 



g. Bacteria may cause abnormal odors and tastes in 



