lOi Dairy Bacteriology. 



fluid. The different methods that have been proposed to 

 accomplish this result depend upon the removal of the con- 

 tained organisms by mechanical means, or their destruc- 

 tion in the milk by means of either chemical or physical 

 processes. In removing the bacteria two means have been 

 more or less extensively employed, as filtration and cen- 

 trifugal force. 



Filtration Of milk. Straining milk through cloth or 

 wire strainers has always been used as a means of cleaning 

 milk from dirt and foreign matter; but it is quite evident 

 that the removal of such material can only diminish the 

 germ content of the milk to the extent that bacteria would 

 adhere to such coarse particles. The individual organisms 

 floating in milk are capable of passing the finest strainer, 

 and consequently, such processes are more accurately meth- 

 ods of cleaning and purifying the milk rather than meth- 

 ods that enhance the keeping quality. 



Along somewhat similar lines are the various methods 

 of filtration that have been devised. The use of germ- 

 proof filters, such as the Pasteur or Berkefeld type, are 

 inadmissible with milk, because the pores of these filters 

 are so fine as to hold back practically all suspended matter, 

 fat and casein as well as the bacteria. 



For a number of years, gravel, sand or quartz filters 

 have been employed for the double purpose of cleaning 

 milk and preserving^ it. Several different types of these 

 filters are or have been in use. The most satisfactory are 

 built in several sections so as to permit of read} r cleansing, 

 a process which must be most thoroughly carried out with 

 apparatus of this kind. Bolle of Berlin washes his filters 

 first with boiling water, then dilute hydrochloric acid, and 

 finally, with water until all trace of acid is removed. The 



