EYES AND FLAVOR IN EMMENTAL CHEESE 387 



while our organism causes an active fermentation of glycerol with 

 the production of a considerable quantity of volatile acids. 

 Finally, it may be stated that the organism with which we have 

 been working causes the typical sweetish flavor in Emmental 

 cheese, whereas the experiments of Von Freudenrich and Orla-Jen- 

 sen did not give definite results on this point. Orla-Jensen 

 (1912) has since stated more conclusively that the sweetish flavor 

 is due to a factor other than the propionic acid bacteria. 



It is of course recognized that an accurate comparison can not 

 be made from pubhshed descriptions. It is hoped, therefore, that 

 we may obtain from European workers cultures of the various 

 types of propionic acid- forming bacteria so as to determine more 

 definitely whether this organism is identical with any of the pre- 

 viously described types or whether it is a new variety. In this 

 connection it may be noted that we have also isolated a variety of 

 these lactate-fermenting bacteria, among which have been found 

 quite distinct types. Although the characteristics of aU of these 

 varieties have not been studied in detail, they appear to agree 

 in a general way with the types which have been isolated by 

 European workers. It is hoped that further studies on these 

 organisms, in comparison with types obtained from Europe, 

 may be made in the future. 



In keeping with the nomenclature used by the European 

 workers for the group of propionic acid-producing bacteria, this 

 organism will be tentatively designated as Bad. acidi-propionici (d) . 



The isolation of cultures 



The direct isolation of this organism from cheese is difficult 

 for various reasons, particularly because of its slow growth and 

 its oxygen requirements. Though not a strict anaerobe it 

 requires a considerably reduced oxygen tension. Although 

 in pure culture this organism grows in all ordinary culture 

 media, including even 1 per cent pepton solution, it is appar- 

 ently not so easy to obtain growths from it when taken directly 

 from cheese. On a few occasions colonies have been isolated 



