68. The Occurrence of Coliform Bacteria in Milk

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Abstract
1. Of 21,569 samples of mixed cow's milk taken under fair conditions of cleanliness and examined by means of the coliform test, 48·3 per cent, gave negative results with 1/10, 1/100 and 1/1000 c.c. amounts; 21–4 per cent, gave positive results with only 1/10 c.c.; 14·0 per cent, gave positive results with only 1/10 and 1/100 c.c.; and 16·3 per cent, gave positive results with 1/10, 1/100 and 1/1000 c.c. It is probable that these results are better than those generally obtained. 2. The proportion of coliform-positive samples was much higher in summer and early autumn than during the winter and spring. This seasonal variation was largely due to atmospheric temperature, there being a well-marked direct correlation between the proportion of coliform-positive samples and the mean of the minimum and maximum atmospheric temperatures. 3. Of 21,857 samples examined, 10,458 were coliform negative and had an average bacterial content of 25,294 per c.c; 11,399 were coliform positive and had an average bacterial content of 160,577 per c.c. The coliform-positive samples contained on an average 6·3 times as many bacteria as the coliform negative.

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