246 AGRICULTURAL BACTERIOLOGY. 



the washing and working of the butter. Large numbers are 

 still left in the butter. Ordinarily these bacteria do not grow 

 in the butter, but, if it is not salted, some of them may grow 

 and hasten its spoiling. Unsalted butter does not keep long 

 and its destruction is largely due to bacteria. But if the 

 butter is salted, as is the rule in most countries, the salt checks 

 the growth of bacteria and indeed prevents the growth of most 

 species. As a result of this and the compact condition of the 

 butter, together with its small amount of water, the bacteria do 

 not find the butter a favorable medium for growth and begin 

 to diminish in numbers. A very few hours' time shows a most 

 extraordinary reduction in numbers, and this continues until, 

 after a few weeks, if the butter is kept so long, the butter con- 

 tains comparatively few bacteria. They do not entirely disap- 

 pear, for some are found even in very old butter. The ordinary 

 species of organisms, which have been active agents in the 

 cream -ripening, cease to grow and play no further part in the 

 changes which may occur in the butter. The following figures 

 of the number of bacteria in butter will illustrate the facts. 



No. OF BACTERIA PER GRAM OF BUTTER. 



2 hours old. i day old. 4 days old. 30 days old. 



54,000,000 26,000,000 2,000,000 300,000 



It is important to notice that the pathogenic bacteria of 

 typhoid fever and tuberculosis remain alive in butter for some 

 time, and certainly long enough to render butter a source of 

 infection should these bacteria be abundant in the original 

 milk. Although this is a theoretical possibility, no instances 

 are known where such an infection has actually occurred, a 

 fact which may be due simply to the difficulty of obtaining 

 evidence upon such a difficult problem. 



It is well known that, if butter is not used immediately, cer- 

 tain changes occur which continue slowly for many weeks. 

 The butter retains its fresh, delicate flavor and aroma for only 



