PART V DECOMPOSITION PRODUCTS OF 

 MILK, BUTTER, AND CHEESE 



1. DECOMPOSITION PRODUCTS OF MILK. 



MILK in the cow's udder is not sterile under ordinary condi- 

 tions, for the milk ducts, even the finest, always harbour a 

 greater or less number of bacteria. The number of bacteria 

 present in the udder is only small ; generally white and yellow 

 micrococci are the chief ones to be found, and these have no 

 effect upon the milk. 1 Whether these bacteria get into the 

 udder through the teat or from the blood is not yet 

 proved, but there are many reasons to support the first view. 

 Under normal conditions the number of bacteria in the udder 

 is relatively small, which is due to the bactericidal power of the 

 tissues of the udder. From the moment that the milk leaves 

 the udder it becomes infected with all sorts of micro-organisms 

 from the air, food, litter, excrement of the animals, etc. 



The majority of the micro-organisms in milk never develop 

 further, for they are overpowered by others which find there 

 conditions more favourable to their development. To the latter 

 varieties belong the lactic acid bacteria, as well as the Goli- and 

 Aerogenes bacteria. After some time the lactic acid bacteria 

 (if the milk has not been well cooled) have so increased that 

 the other species of bacilli cease to develop, and after 36 to 48 

 hours at ordinary temperatures 95 to 100 per cent, of the 

 bacterial flora is composed of these lactic acid bacteria. This 

 happens of course under normal conditions. At higher tem- 

 peratures, e.g. 37 C., the relation is somewhat different, for 

 then the Goli- and Aerogenes bacteria develop most vigorously, 

 and may even overshadow the lactic acid bacteria. When the 

 degree of acidity of the milk, due to the conversion of the milk 

 sugar into lactic acid, has reached about 0'8 per cent., the lactic 



1 Chr. Barthel, " Die Mikroorganismen in der Stallluft, in der frisch 

 gemolkenen Milch und im Enter der Kuh," Milch- Zeitung, 1903, p. 626. 

 Reprinted in pamphlet form by M. Heinsius Nachfolger, Leipzig. 



