6 CLEAN MILK 



over 6o u F. The germicidal action disappears spontaneously in old 

 milk. After 36 hours, when milk is kept at 40 F., there is art 

 increase in the number of germs. Dr. Park found in a sample of 

 milk containing only 3,000 germs in the cubic centimeter, that after 

 24 hours at 42 F. it contained 2,600 germs; after 48 hours 3,6oo> 

 germs; and after 96 hours 500,000 gerrrls to the cubic centimeter- 

 The bacteria in reasonably clean milk (12,000 to 25,000 per c.c.) 

 will multiply some fourfold at 50 F. in 24 hours ; and at about the 

 same rate when kept at 46 F. for 36 hours. The number of germs, 

 in milk kept at 32° F. lessens from day to day for a number of 

 days, then increases. 



When milk is kept at higher temperatures the germs multiply 

 rapidly and it sours and deteriorates correspondingly. It has been 

 shown that very clean milk (containing but 3,000 germs to ther 

 cubic centimeter), if kept for 24 hours at 6o° F., held 180,000 

 germs; if kept at 86° F. for 24 hours it contained 1,400,000 germs; 

 and at 94 F. the germs multiplied so tremendously that at the end 

 of 24 hours the same milk contained 25 billion germs per cubic 

 centimeter. 



All germs require some moisture in order that they may 

 actually grow, but they may exist in large quantities — for a longer 

 or shorter time — in dust. Some require air for their existence,, 

 others do not. 



Sunlight is one of the most powerful enemies of germs, since, 

 few will thrive in sunlight, especially in the presence of fresh 

 air. This explains the value of sunning dairy utensils and of per- 

 mitting the sunlight to enter freely into the barn and dairy. Some 

 germs grow more readily in substances having an alkaline or neutraL 

 reaction; others, as those which cause milk to sour, flourish in an. 

 acid medium, providing the acidity is not too great. 



The most potent factors in destroying germs are intense heat 

 and cold, sunlight and chemicals. A temperature varying from 

 140° to 158 F. will kill most germs— if continued long enough or 



