122 Dairy Bacteriology. 



sense waste products, yet, all of them possess sufficient 

 nutrient value to warrant their use as human food or in 

 animal feeding. When handled carelessly, however, their 

 nutritive value is much lessened by the continued fer- 

 mentations that occur in them. All of these products 

 are rich in bacteria owing either to their age or the treat- 

 ment they have undergone in the manufacture of butter 

 or cheese. It is, therefore, all the more essential that 

 they should be kept in such a manner as to check the 

 continued development of germ-life within them. 



119. Skim-milk. Skimmed milk varies much in its 

 bacterial content, depending upon the way in which the 

 full milk has been treated. Milk from which the cream 

 has been removed by the shallow setting process is usu- 

 ally very rich in germs, and often has so much acid that 

 it is easily recognized by the taste. Where the cream is 

 gathered by the aid of ice-water, the temperature is re- 

 duced to such an extent that the skimmed part is rela- 

 tively poor in bacteria. Separator skim-milk is treated 

 in such a radically different way that it is bacteriologic- 

 ally quite a different product. The skimmed part is sep- 

 arated from the fat when the milk is only a few hours old 

 so that the opportunity for germ growth is relatively 

 slight. 



1 20. Buttermilk. Buttermilk contains a large amount 

 of casein and sugar, and is, therefore, of considerable 

 value for feeding purposes. It is usually very rich in 

 bacteria, sometimes containing even more than ripened 

 cream. Pammel 1 found 1,700,000 germs per cc. in but- 

 termilk, while the organisms in butter were less than 

 half a million. This high content is due to the age of 

 the milk and temperature at which the cream is previously 

 ripened. 



1 Pammel, Iowa Expt. Stat., Bull. 21. 



