40 Dairy Bacteriology. 



relative distribution of bacteria. Eckles and Barnes 1 have 

 reported a series of studies of this sort in which they found 

 from 37 to 56 per cent of the organisms removed from 

 the milk by centrifugal force. An average of their re- 

 sults showed about 29 per cent of total bacterial life in the 

 skim milk, 24 per cent in the cream, and about 47 per 

 cent in the slime. Quantitatively the bacterial content of 

 the slime is always exceedingly high, ranging from tens of 

 millions to billions of bacteria per gram. 



It is surprising that the elimination of snch a consider- 

 able proportion of organisms should not materially en- 

 hance the keeping quality of the purified milk. In the 

 work above reported, although the number of bacteria was 

 diminished 15 to 50 per cent, the diminution in develop- 

 ment of acidity in twenty-four hours in the purified sam- 

 ples was only a few hundredths of one per cent. 



The effect of filtration through sand, gravel and other 

 substances is the same as when the milk is passed through 

 the separator, the aim in all cases being to purify or free 

 the milk from solid impurities that find their way into the 

 milk largely from the animal herself. Comparative experi- 

 ments made by Backhaus and Cronheim 2 on various filter- 

 ing devices show that cellulose yields the best results. 

 Schuppan 8 found the supply of a Copenhagen company 

 that used a gravel filter reduced 38 to 48 per cent. 



Influence of barn air. It is impossible to separate the 

 influence of the air entirely from that of the animal, as 

 the dust particles from the coat of the animal must of 

 necessity pass through the air. 



Germ life cannot develop in the air, but in a dried con- 



> Eckles and Barnes, Bull. 59, Iowa Expt. Stot., Aug. 1901. 

 Journ. f. Landw., 1897,45:223. 

 Cent. f. Bakt., 1893, 13:557. 



