Chapter II 



The Normal and Abnormal Microflora 



of Milk 



A. THE NORMAL FLORA 



MILK fresh from healthy clean cows does not contain many 

 organisms beyond a few from the air, and those which normally 

 occur in and on the udder and teats. These organisms are nearly 

 all micrococci and sarcina forms, most of which are without 

 action on milk, while a few both acidify and peptonise it. Accord- 

 ing to Arthur Wolff 1 , certain alkali producing short rod forms 

 (Bacterium lactis innocuum) rank next to the micrococci in point 

 of numbers, in fresh milk. In appearance, these organisms and 

 their colonies closely resemble the aerogenes bacteria, but they 

 do not ferment sugars, and they render milk feebly alkaline 

 instead of acid without causing any other change. According to 

 Burri and Hohl, Streptococcus liquefaciens is occasionally found as 

 a pure culture in the udders of healthy cows 2 . 



Milk which has been less carefully handled contains, in addition 

 to the above, coli, aerogenes, proteus and hay bacteria, ray fungi, 

 moulds, yeasts, fluorescent bacteria and sometimes also butyric 

 acid bacteria. The coli, aerogenes, proteus and butyric acid 

 bacteria generally come from the dung, the fluorescent bacteria 

 from the water used for rinsing the pails, and the others chiefly 

 from the bedding and the stable dust. If the cattle are on 

 pasture, the fluorescent and sporing bacteria may come from the 

 ground. Curiously enough, the typical streptococci are seldom 

 found in milk fresh from the cow. . According to BartheVs investi- 

 gations 3 , they occur in cow dung with which they are distributed 

 over the fields, being therefore found on all cultivated plants. 

 From the latter they find their way back to the cow, and milk 



1 Inaugural Dissertation, Zurich, 1908. Bacterium lactis innocuum is 

 probably identical with the organism known in the literature as Bacterium 

 alcaligenes. 



2 " Schweitzerische Milchzeitung," 1916, Nos. 3 to 8. 



3 " Landbruks-Akademiens Handlinger och Tidsskrift," 1905, p. 403. It 

 will, however, be necessary to revise these investigations since we have 

 now learnt better to differentiate between the various species of lactic acid 

 bacteria. Thus a large proportion of the lactic acid bacteria of the plants 

 are not streptococci in the narrower sense, but betacocci. 



