28 BTJLLETTX 642, TJ. S. DEPARTMENT OF AGEICULTUEE. 



plains, therefore, the relatively low count found in milk placed in the 

 unsterilized utensils. 



The number of bacteria introduced into milk by unsterilized uten- 

 sils is extremely variable because of the many different ways in which 

 the utensils may be handled. To show the variation other experi- 

 ments were conducted, the results of which are shown in Table 10. 

 In these experiments the manure was removed only twice a week and 

 the cows were dirt} 7 . Under the conditions the average count of 

 30 samples of milk from sterilized utensils was 31,040 bacteria per 

 cubic centimeter, which represents the contamination of the milk, 

 largely by manure, but does not include that from unsterilized uten- 

 sils. Under the same conditions 50 samples of milk were taken, di- 

 rectly after milking, from washed but not sterilized utensils. The 

 average count of this series of samples was 666,520. Deducting 

 31,040, the average count from sterilized utensils, the remainder, 

 635,480, represents the average bacterial contamination per cubic 

 centimeter of milk resulting from unsterilized utensils. Referring 

 to the contamination by unsterilized utensils discussed in the previous 

 experiment and shown in Table 9, it may be seen that the contamina- 

 tion in the two experiments was very different, being in the former 

 relatively low and in the latter very high. 



To show further the variability of the factor of unsterilized uten- 

 sils, another series of samples was examined under the same barn 

 conditions but with utensils treated in a different manner. After 

 milking, the milk was poured from the utensils, but the drainings 

 were allowed to remain. The utensils were placed upright on the 

 floor until the next milking, or about eight hours later, when they were 

 washed in the same manner as in the previous experiments. The 20 

 samples of milk taken under these conditions averaged 1,667,000 

 bacteria per cubic centimeter, as shown in Table 10. The count was 

 nearly three times that of the average of 50 samples in which the 

 utensils were washed immediately after milking but not sterilized. 

 By deducting the average figure of 31,040 bacteria obtained in the 

 samples from sterilized utensils, the average number introduced from 

 unsterilized ones held eight hours before washing was about 1,635,000 

 bacteria per cubic centimeter. While that method of handling uten- 

 sils may not represent average conditions in practice, it is not unu- 

 sual. The results indicate that a very large number of bacteria may 

 be introduced into milk from washed, unsterilized utensils. 



