THE RELATION OF MICROORGANISMS TO CHEESE 427 



to which was given the name casease. A chemical study of the by- 

 products of the organisms, when growing in milk, revealed a number 

 of compounds that had previously been found in ripe cheese, such as 

 leucin, tjrrosin, and the ammonia salts of acetic, valeric and carbonic 

 acids. The cultures often possessed a cheese-Uke odor. These facts 

 led Duclaux to believe this class of organisms were responsible for the 

 ripening of the hard cheese in question. The generic name Tyrothrix 

 was applied on account of the supposed relation to cheese. This term is 

 still found in current bacteriological Uteratu^e. The methods employed 

 by Duclaux were such as favored the growth of the liquefying, rather 

 than the acid-forming bacteria. To the latter more recent investi- 

 gators have devoted attention. 



The theory that the proteolytic bacteria function in the ripening 

 of hard cheese has been more recently emphasized by Adametz. It 

 is sufficient to say that the number of spore-forming proteolytic bac- 

 teria in cheese is not sufficiently large, nor is their presence so constant 

 that any importance can be attached to them. Any agent to be con- 

 sidered as a factor in the ripening process must be present in every 

 cheese in sufficient numbers to account for the change for which it is 

 considered responsible. Such agents should be capable of demonstra- 

 tion. It should be remembered that, by following the rules laid down 

 by the practical maker, a normal cheese can invariably be made, 

 hence the factors of importance in the ripening must be constantly 

 present in the milk or rennet. It is doubtful whether the liquefying 

 bacteria will satisfy this requirement. It has been shown by de 

 Freudenreich that such organisms, even when added to milk in large 

 numbers, exert no influence on the ripening of hard cheese, since the 

 conditions within the cheese are not such that growth can occur. 



De Freudenreich, a Swiss microbiologist, by the aid of modern 

 methods, demonstrated the constant presence of certain classes of 

 acid-forming bacteria in Swiss cheese, and to them ascribed an impor- 

 tant r61e in the ripening of this hard cheese. He was led to this con- 

 clusion by their great numbers in the fresh cheese, and by the fact 

 that cheese made from milk drawn under aseptic conditions, which 

 thus contains no lactic bacteria, do not ripen; through the discovery, 

 also, that certain of the lactic bacteria, predominating in Swiss cheese, 

 those of the Bact. bulgaricum group, exert a solvent effect on the 

 casein of milk, although they are devoid of acti6n on gelatin. 



