ABNORMAL CHANGES IN MILK 377 



(b) The best known representatives of this group are B. coli 

 communis and Bad. lactis aerogenes. These organisms give to milk 

 a sharp tang and are the particular enemies of the cheese maker as 

 they are the cause of gassy curd. They are especially numerous in 

 milk which is produced and handled under unsanitary conditions 

 and in such milk outnumber those of Group a, but the rapid growth 

 and acid production of Group a soon checks them. 



(c) This is represented by Bacillus bulgaricus and the rod-shaped 

 organisms which have been especially studied by de Freudenreich. 

 They produce a curd which is easily broken by shaking and shows no 

 tendency to express whey. They give to the milk a pleasant acid 

 flavor and are desirable. 



(d) Acid-forming Udder Bacteria. These are the characteristic 

 bacterial flora of the healthy udder and consist mainly of cocci with 

 few bacilli. They are slow growers and may curdle milk, but the 

 curd so formed resembles that formed by rennet. They produce 

 acetic, propionic, butyric, and caproic acid but no lactic acid. 

 They are an unimportant group of organisms, so far as the" milk 

 is concerned. 



2. Peptonizing Bacteria. These organisms digest the casein 

 either with or without coagulation at times with the formation of 

 an alkaline reaction. Most of these are bacilli of various shapes 

 and sizes, some of them being the largest organism found in milk. 

 There are both motile and non-motile varieties. Many develop 

 very strong putrefactive odors. Barny or cowy odors are caused by 

 this type of bacteria. They are all undesirable and their presence 

 in milk indicates unsanitary condition of production and handling. 



3. Bacteria Producing Milk of Unusual Character. Occasionally 

 bacteria which produce abnormal changes or so-called " diseases' ' 

 of milk find their way into milk from unclean surroundings. They 

 produce various queer milks, for example, red, blue, and green. 

 Sometimes milk develops a bitterness after it is drawn. This is due 

 to the products from a number of bacteria and yeast. At other times 

 milk is changed to a slimy or ropy consistency and may at times 

 result in considerable economic losses. These organisms are quite 

 resistant to heat and frequently pass uninjured through the ordinary 

 methods of cleaning and scaldings. Because of this, dirty utensils 

 once infected become a constant source of infection. 



4. Inert Organisms. These are mostly cocci which produce no 

 appreciable change in milk and are unimportant. 



5. Pathogenic Bacteria. This class consists of the pathogenic 

 bacteria, B. dysenteric shiga, B. dysenteric flexner, B. typhosus, B. 

 paratyphosus a. and B. paratyphosus ., V. cholerc, Bact. diphtheria, 

 Bad. tuberculosis, B. lactimorbimic melitensis. These organisms 

 produce no perceptible change in the milk in which they grow but 

 are dangerous and may give rise to epidemics. 



