CHAPTER XV 



THE GROWTH OF BACTERIA IN FOODS 



Bacteria in Milk 



It is more difBcult to maintain a supply of good milk 

 than of almost any other food product. This is due to 

 three reasons : (i) the number of bacteria, under ordinary 

 circumstances, is greater than in any other food product; 

 (2) milk furnishes an exceptionally favorable food for 

 bacteria; (3) the changes which these bacteria produce in 

 milk are very decided and take place with great rapidity. 

 These three factors together make it flifficult to preserve 

 milk in the household without exceptional precautions. 



The bacteria present in milk are not only numerous 

 but comprise many kinds (Fig. 66). Milk may contain 

 bacteria while still in the udder, and it has a further 

 chance of contamination with microorganisms from a vari- 

 ety of sources, so that a few minutes after the milk has 

 been djawn it may contain organisms in large numbers. 

 The chief sources of these organisms are (i) the bacteria 

 in the milk ducts, which are washed into the milk can 

 during the milking; (2) the dust that is likely to be float- 

 ing in the air of the bam or milking stall where the milk 

 is drawn ; (3) the milk vessels, which are rarely washed 

 perfectly clean; (4) the dirt and filth that are always 

 clinging to the hairs of the cow and which fall into 



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