4 SCIENCE AND PRACTICE OF CHEESE-MAKING 



When milk is not properly cared for by patrons, it 

 may acquire undesirable characteristics, which injure 

 its usefulness in cheese-making, such, for example, as 

 high acidity, offensive odors and tastes, formation of 

 gases, etc. 



The causes of these defects will be briefly con- 

 sidered under four headings: (i) Bacterial infec- 

 tion, (2) absorption of flavors, (3) food eaten, (4) 

 physiological or disease processes in cows. 



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FIG. 1 



Appearance of clean milk under 

 the microscope. Only fat^globules 

 are seen. 



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FIG. 2 



Appearance of unclean milk vmder the 

 microscope. The lisrht, round bodies are 

 fat-globules; the dark masses are groups 

 of bacteria and cellular matter. 



SOURCES OF BACTERIAL INFECTION 



Milk, when drawn with careful precautions from 

 the udder of a cow, contains comparatively few 

 bacteria; but milk obtained and handled under ordi- 

 nary conditions is found to contain large numbers, 

 often several hundred thousand, in one cubic centi- 

 meter (somewhat less than one-quarter of an ordinary 

 teaspoonful). The more dirt there is in milk, the 



