CHAPTEE XLV. 



THE BACTERIOLOGY AND THE BACTERIOLOGIC EXAMINATION 

 OF MILK 1 GENERAL INTRODUCTORY CONSIDERATIONS 

 THE CHANGE OF LACTOSE INTO LACTIC ACID 

 LACTIC-ACID BACTERIA ANAEROBIC BUTYRIC- 

 ACID FORMERS PEPTONIZING BACTERIA 

 ALCOHOLIC FERMENTATION 

 OF MILK. 



GENERAL INTRODUCTORY CONSIDERATIONS. 



WHILE milk is an excellent culture medium for many bacteria, 

 there are also many which do not find in milk conditions favorable 

 to their growth. It is practically impossible to obtain milk from 

 animals in an absolutely germ-free or sterile condition. This statement 

 can perhaps best be explained by the analogy of surgeons 7 attempts 

 to obtain completely germ-free hands before an operation. Such 

 endeavors were begun soon after the knowledge of pyogenic wound 

 infection microorganisms and their ubiquitous nature became estab- 

 lished and have been continued for several decades. A vast litera- 

 ture upon this subject has accumulated, but notwithstanding trials 

 continued for many minutes up to one-half hour and more it is now 

 conceded to be impossible to sterilize the human hands. While 

 washing and scrubbing with disinfectants, such as soap and water, 

 dilute alcohol and corrosive sublimate solution may render the surface 

 of the hands temporarily germ free, the cracks and recesses of the 

 skin and the ducts of the sweat and sebaceous glands remain infected 

 with bacteria, which when the hands are used and when perspiration 

 occurs soon find their way to the surface. 



This being the case it would be unreasonable to expect that the 

 external surface of the udder and the hands of the milker could be 

 so sterilized as to render them entirely free from bacteria. Even 

 were this possible the bacteria always occurring in the milk-ducts still 

 remain, and they would find their way into the milk during milking. 

 For this reason it may be stated that milk after collection is practically 



1 The bacteriology and hygiene of milk have been treated as fully as is consistent in a text- 

 book on bacteriology. For a more extensive consideration the reader is referred to the following 

 works: Sommerfeld, Handbuch der Milchkunde, Wiesbaden, 1909; Jensen, Essentials of 

 Milk Hygiene, translated by Pearson, Philadelphia, 1909; Conn, Bacteria in Milk, Phila- 

 delphia, 1903; Swithinbank and Newman, Bacteriology of Milk, New York, 1903; Milk and 

 its Relation to Public Health, Public Health and Marine Hospital Service of the United 

 States, Washington, Bulletin No. 56; Russel, Outlines of Dairy Bacteriology; Ward, Pure 

 Milk and the Public Health; Winslow, Clean Milk. 



