BACTERIA IN OUR DAIRY PRODUCTS. 771 



of them after the churning ? The answer to these questions is 

 simple. Many of the bacteria go off in the buttermilk; many 

 more are removed by the water used in washing, but many of 

 them still remain in the butter. Here, however, their active 

 life is nearly over, for the salt added to the butter checks their 

 growth and their numbers begin to diminish. Butter is not a 

 good medium for their development, and, after a few weeks, they 

 practically disappear. Their growth in the butter is thus so 

 slight that it is of no importance and ordinarily produces no no- 

 ticeable result. To be sure, the butter may subsequently become 

 rancid, and until recently it has been supposed that the rancidity 

 of butter was due to bacteria growth. Some species of bacteria 

 certainly produce butyric acid, and this is one of the most promi- 

 nent characteristics of rancid butter. But it has been recently 

 shown that butter may become rancid independently of bacteria 

 growth, the direct oxidizing power of the air producing the effect. 

 Bacteria, it is true, may hasten the process, but they are probably 

 not a necessary cause. After the butter is made, then, the bac- 

 teria are of no further importance, and unless there should chance 

 to be some disease-germs among them nothing further will result 

 from their action. 



The butter-maker thus forces the bacteria to give to his butter 

 a flavor for which he gets a good price in the market. Unfortu- 

 nately for him, however, there is more than one species of bac- 

 teria which may readily get into his cream and produce its ripen- 

 ing, and not all of them are equally serviceable to him. Many 

 species of bacteria give a very unpleasant flavor to the butter if 

 they are abundant in the ripening cream. While they cut the 

 slime that holds the fat-globules and thus make the churning 

 easy, the aroma produced by different species is by no means 

 always satisfactory. It has been found that many of the species 

 which commonly grow in ripening cream will produce very dis- 

 agreeable butter if they are allowed to act alone. Others acting 

 alone produce good butter, and the latter must, of course, out- 

 weigh the former, or the butter will be unsatisfactory. 



The fact is, that during the ripening of the cream a great bat- 

 tle is going on among the different species of bacteria. Some of 

 them find the conditions of the ripening cream favorable to their 

 growth, while others find it less favorable. The favored species 

 multiply rapidly, and may largely crowd out of existence those 

 less favored. Some species may chance to get the start of oth- 

 ers by being in greater numbers at the outset, while another spe- 

 cies will make up for all drawbacks by having a more rapid rate 

 of multiplication. The final result of the struggle will depend 

 upon an infinite variety of conditions, which will be entirely be- 

 yond our knowledge. The condition of the cow, the manner of 



