58 



BULLETIN 642^, U. S. DEPARTMENT OF AGRICULTURE. 



Table 28. — Ratio of growth of bacteria in milk when held at 15.5° C. (60° F.) 

 and 21.1° C. {70° F. ) —Continued. 



MILK PRODUCED UNDER DIRTY CONDITIONS IN UNSTERILIZED UTENSILS. 



1 





1.4 

 5.6 

 4.5 

 4.9 

 5.3 

 1 



1.2 

 7.6 

 13.6 

 15.1 

 10 

 2 

 2.5 



16.6 

 97.3 

 81.9 

 21 



36.6 

 37.5 

 31.2 

 142.1 

 136.4 

 1,183.7 

 2, 622. 2 

 123.3 

 82.1 





5.3 



8.4 



9.3 



7.5 



6.2 



3.4 



30.9 



17.7 



108.3 



63.7 



76.1 



8.2 



7.1 



4,495.4 

 302.6 

 510.6 

 577.9 

 67.4 

 41.4 

 112.1 





2 



1,111.8 



446.8 



1,082.5 



12.6 



90.6 



342.4 



691.8 



11,710.5 



3 



3,989.3 

 422 



4... 



5 



280.5 



6 



298.3 



7. 



5, 636. 3 



8 



2,201.2 



9 



1. 187. 5 

 702.7 



5,333.3 



2. 666. 6 

 1,250 





10 



5, 729. 7 

 5, 555. 5 

 3,750 



49, 729. 7 



11 



83, 333. 3 



12 



173,333.3 



13... 

















5. 7 



354.7 



1,881.3 



27 



1, 437. 3 



33,093.4 









SUMMARY. 



1. Milk of low bacterial content and practically free from visible 

 dirt, when fresh, was produced in an experimental barn under condi- 

 tions similar to those on the average low-grade farm. 



2. Three simple factors were necessary for the production of milk 

 with a low bacterial content, namely, sterilized utensils, clean cows 

 with clean udders and teats, and the small-top pail. A fourth factor, 

 holding the milk at a temperature near 10° C. (50° F.) or lower, is 

 necessary in order to keep the bacterial content low. 



3. The average count of 65 samples of fresh milk produced by the 

 aid of the three factors, except that the udders and teats were not 

 washed, was 4,524 bacteria per cubic centimeter. The average count 

 of milk directly from the udder was 757 bacteria per cubic centi- 

 meter: the difference of 3,767 therefore represents the number intro- 

 duced through external contamination. During the same period 

 when the udder and teats of the cows were washed, the average of 

 the 65 samples was 2,154 bacteria per cubic centimeter, and as the 

 average udder count was 739, the difference, 1,415 bacteria, repre- 

 sented those added through external contamination. 



Washing the udder and teats of the cows not only caused a decrease 

 in the bacterial content of the milk but also more nearly uniform 

 counts. 



A study of the bacterial groups in the low-count milk showed that 

 they correspond closely to those in the milk drawn directly from the 

 udder. 



4. A practical demonstration of the value of the three essential 

 factors was made on six farms. The results indicate that it is pos- 

 sible for the average farmer with inexpensive equipment to produce 

 milk of low bacterial content with little extra work. 



5. The results indicate that in general the greatest contamination 

 of milk comes from the use of unsterilized utensils. The simple steam 



