BACTERIA IN MILK 1043 



of cream, or the addition of antiseptics, absolutely prevents cheese 

 production. 



The organisms which arc concerned in such processes have been 

 extensively 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 protein composition; in the latter, reten- 

 tion of whey gives rise to cultural 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 50 attributed the "ripen- 

 ing" of some of the soft cheeses to a microorganism closely related 

 to Bacillus subtilis. V. Freudenreich 51 in part substantiated this, 

 but laid particular stress upon the action of Oidium lactis, a mold, 

 and upon several varieties of yeast. Conn, 52 more recently, in a 

 bacteriological study of Camembert cheese, has demonstrated that 

 the production of this cheese depends upon the united action of two 

 microorganisms, one an oi'dium, like the Oidium lactis of Freuden- 

 reich, 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 work of these men and 

 of others has seemed to place cheese production, attempts at uni- 

 formity in cheese production have met with almost insuperable 

 obstacles because of the presence of a variety of adventitious micro- 

 organisms which, depending in species and proportion upon the local 

 conditions under which the various cheeses have been produced, 

 have added minor characteristics of flavor which have determined 

 market value. Occasional failure of good results in cheese produc- 



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



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



*-C&nn, Bull. Statis. Agri. Exp. Stat. 35, 1905. 



