1042 BACTERIA IN AIR, SOIL, WATER, AND MILK 



variety of lactic-acid bacilli is present and these, as in milk, outgrow 

 other species and, according to Conn, 44 are probably essential for 

 ' ' ripening. ' ' 



It would be of great practical value, therefore, if definite pure 

 cultures of the bacteria which favor the production of agreeable 

 flavors could be distributed among dairies. In Denmark this has 

 been attempted by first pasteurizing the cream and then adding 

 a culture of bacteria isolated from " favorable " cream. These cul- 

 tures, delivered to the dairyman, are planted in sterilized milk, in 

 order to increase their quantity, and this culture is then poured 

 into the pasteurized cream. In most cases, these so-called " starters" 

 are not pure cultures, but mixtures of three or more species derived 

 from the original cream. 



Adverse accidents in the course of butter-making, such as "sour- 

 ing" or "bittering" of butter, are due to the presence of con- 

 taminating, probably proteolytic, microorganisms in the cream 

 during the process of "ripening." 



As a means of transmitting infectious disease, butter is of im- 

 portance only in relation to tuberculosis. Obermuller, 45 Rabino- 

 witch, 46 Boyce, 47 and others, have repeatedly found tubercle bacilli 

 in market butter, and Mohler, 48 Washburn, and Rogers have recently 

 shown that these bacilli could remain alive and virulent for as long 

 as five months in butter kept at refrigerator temperature. The 

 acid-fast butter bacillus, described by Rabinowitch as similar to 

 the true Bacillus tuberculosis, shows decided cultural and mor- 

 phological differences from the latter. 



Bacteria and Cheese. The conversion of milk products into 

 cheese consists in a process of protein decomposition which, by its 

 end products, leucin, tyrosin, and ammonia compounds, largely 

 determines the cheese-flavors. The production of cheese, therefore, 

 is due to the action of proteolytic bacterial enzymes 49 and the variety 

 of a cheese is largely determined by the microorganisms which are 

 present and by the cultural conditions prevailing. The sterilization 



"Conn, "Agricultural Bacteriology," Phila., 1901. 

 45 Obermuller, Hyg. Eundschau, 14, 1897. 

 * Rabinowitch, Zeit. f. Hyg., xxvi, 1897. 



47 Boyce and Woodhead, Brit. Med. Jour., 2, 1897. 



48 Mohler, U. S. P. H. and Mar. Hosp. Serv. Bull. 41, 1908. 



49 Freudenreich, Koch's Jahresbericht, etc., 135, 1891. 



