132 BACTERIOLOGICAL METHODS 



milk, is tlie Streptococcus lacticus of Kruse. The Bacillus (lactis) 

 aerogenes which is very closely similar to Bacillus coli, also sours 

 milk and is likely to be present at the beginning of the fermenta- 

 tion. The common pus streptococci and staphylococci are often 

 found in milk in large numbers, traceable to dirt and filth and to 

 diseased udders and less commonly to the hands of the milkers. 

 The colon bacillus when present is traceable to stable dust and 

 manure and to the unclean hands of the milkers. 



The following are some of the organisms which cause diseases 

 of milk: 



1. Bacillus cyanogenes — Blue milk. 



2. Bacillus prodigiosus — Red milk. 



3. Bacillus erythrogenes — Red milk. 



4. Bacillus synxanthus — Yellow milk. 



5. Torula amara — Bitter mUk. 



6. Streptococcus hollandicus — Ropy milk. 



Naturally the bacilH normally present in the milk which is 

 stored for cream formation are also present in the cream after the 

 skimming and cause the so-called ripening of the cream. In 

 order that the ripening process may proceed in a desirable manner, 

 the objectionable butyric acid formers must be excluded. The 

 butyric acid formers are more generally associated with filth, hence, 

 a careful compliance with sanitary rules and regulations in the 

 dairying establishment will generally encourage the invasion and 

 development of the desirable lactic acid organisms to the exclusion 

 of the undesirable microbes, though this is by no means always 

 the case. Occasionally, even with the most scrupulous adherence 

 to sanitation, cream will not ripen properly and these occasional 

 failures have prompted the more progressive dairymen to in- 

 oculate the milk and cream with pure cultures of the desirable cream 

 ripening bacilli. Others use natural cream starters, that is, small 

 quantities of old cream which has ripened with a desirable flavor. 



Cream should not show colon bacilli in less than o.io cc. quanti- 

 ties and fresh unripened cream should not contain more than 5,000,- 



