292 REPORT OF OFFICE OF EXPERIMENT STATIONS. 



monts also showed tlio marked inflnonce of a tomporatiiro of 50° in 

 checking bac-terial ^i-owth and iiiij)r()vinp the kccpiii*; (luality of the 

 milk as compared witli the higher temperature employed. 



HANDLING MILK. 



While milk ordinarily receives the jj^reatest amount of contamina- 

 tion durin<r the i)rocess of milking, later contaminations are b}' no 

 means insignificant and are often of the greatest danger, as wheu 

 typhoid and other pathogenic bacteria gain access to milk through 

 the want of cleanliness in handling. 



Straining removes a certain amount of dirt, as has been noted. 

 Conn and Stocking" at the Connecticut Storrs Station studied the 

 effect of straining through two layers of sterilized cheese cloth upon 

 the bacterial content and keeping quality of the milk. Straining 

 apparently had no very marked effect upon the number of bacteria 

 nor the time required for curdling. The bacterial contamination of 

 milk bv the use of unclean strainers is a matter of common comment, 

 yet it nevertheless is of very frequent occurrence. Very little experi- 

 mental work on filtering milk occurs in station literature. 



The purification of milk b}^ means of centrifugal separators has 

 been subjected to some experimental tests at the stations. In this 

 method the milk is run through the separator in the usual way, and 

 the skim milk and cream are then mixed, while the solid impurities 

 are for the most part removed as separator slime. Some attention 

 has been paid to the effect of separation upon the bacterial content 

 of milk. Eckles and Barnes ^ found that the reduction in the number 

 of bacteria due to separation varied in seven experiments from 15 tx) 

 51 per cent, and that the acidity of the separated milk was slightly 

 less at the end of twenty-four hours than that of the unseparated 

 milk. They concluded, however, that separation improved the keep- 

 ing quality of the milk little, if any. Doane '" found that in four out 

 of five trials the acidity of fresh samples of milk w^hich had been 

 separated and mixed was greater than that of the unseparated 

 samples and concluded that the use of the separator for removing 

 dirt from milk tends to lessen rather than improve the keeping quali- 

 ties of the milk. Erf and Melick'* obtained a reduction of one-fifth 

 to one-fourth of the number of bacteria in running milk through a 

 properly cleaned separator. Those results are in accord with general 

 experience that, Avhile centrifugal separation may remove a large 

 proportion of the dirt in milk, it is incapable of removing bacteria 



o Connecticut Storrs Sta. Rpt. 1903, pp. 33, 38. 



& Iowa Sta. Bui. 59, p. 55. 



c Maryland Sta. Bui. 88, p. 126. 



<iKausas Sta. Bui. 131. 



