Bacteria in the Cheese Industry. 159 



able time. Even where added in large numbers to the 

 curd, they soon perish. 



While the by-products of proteid decomposition induced 

 by this class of bacteria are very similar to those found 

 in a well-ripened cheese, still the above facts have seemed 

 an insuperable barrier to the general acceptance of this 

 explanation . 



167. Lactic acid theory. It has already been shown 

 that the lactic acid species seem to find in the green cheese, 

 the optimum conditions of development, that they increase 

 enormously in the cheese for a short period, and then 

 finally decline in numbers. This marked development 

 coincident with the breaking down of the casein, has led 

 to the view that has been so ably expounded by Freud- 

 enreich 1 that this type of bacterial action is concerned 

 in the ripening of cheese. This group of bacteria are 

 unable to liquefy gelatin, or digest milk, or, in fact, to 

 exert under ordinary conditions any proteolytic or 

 peptonizing properties. This has been the stumbling- 

 block to the acceptance of this hypothesis as an ex- 

 planation of cheese-ripening. Freudenreich has recently 

 carried on experiments that he believes solves the prob- 

 lem. By growing cultures of these organisms in milk 

 to which sterile, freshly precipitated chalk had been 

 added, he was able to prolong the development of bac- 

 teria for a considerable period of time, and as a result 

 of this, he finds that an appreciable part of the 

 casein is digested. Weigmann 2 inclines to the view that 

 the lactic acid bacteria are not the true cause of the pep- 

 tonizing process, but that their development guides or 

 directs the character of the ripening by giving favorable 

 conditions for the development of other species. 



1 Freudenreich, Landw. Jahr. d. Schweiz, p. 85, 1897. 



2 Weigmann, Cent. f. Bakt., II. Abt., 4: 593, 1898. 



