48 Dairy Bacteriology. 



ture of 48-50 F., it is possible to chill milk sufficiently to 

 keep it. Where cold water is not available, ice water 

 should be used. In the production of the best quality of 

 milk for the factory, this factor of early and thorough 

 cooling is entitled to more weight than even the matter of 

 extreme care in milking. 



Mixing: night and morning milk. Common experience 

 has often shown when old milk is mixed with new, that 

 the fermentative changes are more rapid than would have 

 been the case if the two milks had been kept apart. This 

 is most frequently observed when the night milk is cooled 

 down and mixed with the warm morning milk. This 

 often imperfectly understood phenomenon rests upon the 

 relation of bacterial growth to temperature. The night 

 milk may be cooled down to 50 F., but by the next morn- 

 ing it has considerably more bacteria than the freshly 

 drawn sample, the temperature of which may be 90 F. 

 Now, if these two milkings are mixed, the temperature of 

 the whole mass will be raised to a point that is more fa- 

 vorable for the growth of all of the contained bacteria 

 than it would be if the older milk was kept chilled. 



Number of bacteria in milk. The germ content of 

 milk varies so greatly that unless the conditions are all 

 known, it is impossible to foretell what may be found 

 therein. An examination of milk will often reveal a dif- 

 ference in numbers, ranging from a few score of germs to 

 hundreds of millions per cc. The presence of such a vary- 

 ing number is dependent upon certain factors, as the age 

 of the milk, the care taken during the milking, and also 

 the way in which it has been handled since that time. 

 Disregarding milk of different ages, the number of germs 

 present in any sample bears a general relation to the 



