PRODUCTION OP MILK OF LOW BACTERIAL CONTENT. 45 



evidence of great contamination, is evidently not due in most cases to 

 original contamination. The results show that extremely high counts 

 in milk are in general the result of bacterial growth rather than 

 original contamination. 



THE EFFECT OF TEMPERATURE ON THE GROWTH OF BACTERIA 



IN MILK. 



The results shown in the previous discussion of the factors essen- 

 tial for the production of milk of low bacterial count when fresh 

 apply only to fresh milk. The dairyman must remember that when 

 milk of that kind has been produced his responsibility has not ended, 

 for the milk must be kept cold to prevent the growth of bacteria. 

 The three factors discussed prevent to a large degree the contamina- 

 tion of milk during production, as the term is used in this bulletin. 

 In the broad sense of the term "production of milk," the effect of 

 temperature at which the milk is held on the farm must also be con- 

 sidered. It is one of the greatest problems in the handling of milk 

 on the farm, and extensive studies have been made to show the effect 

 of holding milk at different temperatures -during varying lengths of 

 time. Samples of milk produced under different conditions were 

 held at 4.4°, 10°, and 15.5° C. (40°, 50°, and 60° F.) and examined 

 when fresh and after each interval of 24 hours for 96 hours, or 4 

 days. The milk was produced in the experimental barn under three 

 different sets of conditions, as follows: 



First. Cows were clean and bedded ; the udders washed part of the 

 time and left unwashed part of the time; the small-top pail used; 

 and all utensils were sterilized. 



Second. Cows were dirty : the manure was removed twice a week ; 

 both open and small-top pails used ; and all utensils were sterilized. 



Third. Conditions same as second except that the utensils were not 

 sterilized. 



Complete detailed results showing the growth of the bacteria in 

 the milk produced under the different conditions mentioned are given. 

 Twenty samples produced under condition 1 were studied ; 34 samples 

 under condition 2, and 30 under condition 3. 



The bacterial development in milk having a low count, as described 

 under the first condition, is shown in Table 20. The calculated ratio 

 of the bacterial growth in each sample is shown in Table 21. The 

 bacterial development in milk under the second condition mentioned 

 is shown in Table 22 and the ratio of the bacterial development in 

 Table 23. Tables 24 and 25 show similar results for milk produced 

 under the third condition. The summary of the averages of all the 

 samples studied during this work is shown in Table 26. It will be 

 noted that the milk produced under the three conditions when fresh 

 showed somewhat different bacterial counts; that produced under 

 condition 1 averaged 4,295 bacteria per cubic centimeter; under con- 

 dition 2, 39,082; and under condition 3, 136,533. It will be seen, 



