30 CHANGES IN MIIvK CAUSED BY BACTERIA. 



tures putrefaction goes on slowly, so that this circumstance is 

 of no practical importance in the care of milk as customarily- 

 kept for consumption. A very old milk, however, even though 

 it has been kept at 12°C. and not sour, may not be free from 

 the products of putrefaction. 



Source of putrefactive organisms . The dust of stable air, 

 and particularly the filth dropping into the milk pail from the 

 udder and flanks of the cow, certainly contribute liberally to in- 

 fection by putrefactive organisms. Poorly cleansed milk uten- 

 sils and polluted water deserve mention. In fresh milk these 

 organisms greatly outnumber the lactic acid organisms. 



Toxic milk. There are on record a few cases of poisoning 

 believed to have been due to the elaboration of toxic substances 

 by bacteria in milk. Very little is known about the topic. 

 Kastle (21) has made a summary of the subject and has col- 

 lected a bibliography. 



Ropy milk. None of the faults of milk arouse the distrust 

 of the consumer more than the viscid condition of milk and 

 cream, popularly designated "ropy." The widespread abhor- 

 rence of milk in this condition is induced by the belief that 

 it is the product of a diseased udder. The false inference 

 is encouraged by the fact that dairymen sometimes refer to the 

 milk of an inflamed udder as "ropy" or "stringy." There 

 is no relation between the two and no real confusion beyond 

 that induced by the double significance of the word ropy. 

 There is no ground for attributing a harmful result from the 

 consumption of the ropy milk delivered to customers, but the 

 occurrence of the trouble menaces the success of a milk route 

 by occasioning loss of custom. 



The viscid condition appears not sooner than twelve hours, 

 but sometimes as late as thirty hours, after milking. Further- 

 more, it is most readily observed in milk that has stood undis- 

 turbed for several hours, during which period the cream has 

 risen. These conditions give the false impression that the 

 trouble is only associated with cream, while, in fact, skim 

 milk is just as susceptible to the trouble. The consistency of 

 cream does, however, accentuate the viscosity. Fig. 5 shows 

 the behavior of ropy cream when lifted with a fork. 



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