714 BACTERIA IN AIR, SOIL, WATER, AND MILK 



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 morphological differences from the latter. 



Bacteria and Cheese. The conversion of milk products into cheese 

 consists in a process of proteid 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 1 and the variety of a cheese is largely 

 determined by the microorganisms which are present and by the cul- 

 tural conditions prevailing. The sterilization of cream, or the addition 

 of antiseptics, absolutely prevents cheese production. 



The organisms which are concerned in such processes have been ex- 

 tensively studied and attempts have been made, with moderate success, 

 to produce a definite flavor with pure cultures. 



In the production of cheese the two varieties, hard and soft cheeses, 

 depend not so much upon the bacterial varieties as upon the differences 

 in the treatment of the curds before bacterial action has begun. In the 

 former case, a complete freeing of the curds from the whey furnishes a 

 culture medium which is comparatively dry and of almost exclusively 

 proteid composition; in the latter, retention of whey gives rise to cul- 

 tural conditions in which more rapid and complete bacterial action may 

 take place. The holes, which are so often observed in some of the hard 

 cheeses, are due to gas production during the process of "ripening." 



As to the varieties of microorganisms present in various cheeses, much 

 careful work has been done. Duclaux 2 attributed the " ripening" of 

 some of the soft cheeses to a microorganism closely related to Bacillus 

 subtilis. V. Freudenreich 3 in part substantiated this, but laid particular 

 stress upon the action of Oidium lactis, a mold, and upon several vari- 

 eties of yeast. Conn, 4 more recently, in a bacteriological study of Cam- 

 embert cheese, has demonstrated that the production of this cheese 

 depends upon the united action of two microorganisms, one an oidium, 

 like the Oidium lactis of Freudenreich, which is found chiefly in the 

 interior softened areas, the other a mold belonging to the penicillium 

 variety, found in a matted felt-work over the surface and penetrating 

 but a short distance. In spite of the scientific basis upon which the 



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



2 Duclaux, "Le Lait," Paris, 1887. 



3 V. Freudenreich, Cent. f. Bakt., II, i, 1895. 



4 Conn, Bull. Statis. Agri. Exp. Stat. 35, 1905. 



