BACTERIAL FLORA OF RIPENING CHEESE 245 



the following conclusion : " The ripening of cheese I hold to be a true fermen- 

 tation." This fermentation he ascribed to the organisms ("lab-bacilli") present 

 in the rennet liquid, and which he associated with the bacteria then grouped 

 under the name Bacillus suUilis, a general term not to be confounded with that 

 at present applied to an entirely distinct species. Cohn's decision was based 

 exclusively on the microscopical examination of rennet and cheese ; and the same 

 applies also to the statements of F. BENECKE (I.) 



It was not until 1878, however, that attempts were made to obtain pure cultures 

 of the presumptive cause of the ripening of cheese, and to test the influence of 

 the organism. This was effected by E. DUCLAUX (VII. and XIII.) in his studies on 

 Cantal cheese, from which he isolated ten species of Schizomycetes and classified 

 these under the common generic name of Tyrothrix belonging to the large sub- 

 group of the so-called hay and potato bacilli. Out of these ten species, one, 

 T. virgula, being unable to grow in milk, will be omitted from further considera- 

 tion. Each of the remaining nine produces two classes of enzymes, one resembling 

 lab and coagulating milk, whilst the other, casease ( 147), dissolves and splits up 

 the albumin thus precipitated. This proteolytic enzyme can be thrown down from 

 the bacterial cultures by means of alcohol. A particularly abundant yield is 

 obtained from Tyrothrix tenuis, an actively motile, sporogenic rod about 0.6 p. 

 broad and 3 p. long, and often growing in the form of filaments ; hence the name 

 Tyrothrix (= cheese-thread, cheese-hair). This species is aerobic, as are also 

 T. Jiliformis, T. distortus, T. geniculatus, T. turgidus, and T. scaber ; whilst T. 

 urocephalum, T. claviformis, and T. catenula are, on the other hand, anaerobic. 

 Cultures of Tyrothrix tennis obtained from Duclaux' laboratory were investigated 

 in 1895 by W. WINKLER (I.), who formed the opinion that this species can be 

 modified, by cultivation, into three varieties or races. This was, however, 

 contradicted by J. WITTLIN (I.) in 1896. 



The metabolic products, e.g. leucine, tyrosine, and the ammonia salts of 

 acetic, valeric, and carbonic acids yielded by the Tyrothrix species are the 

 identical substances we have seen to be produced in the ripening of cheese. 

 This concordance necessarily strengthens Cohn's hypothesis, that the ripening of 

 cheese is effected by the vital activity of micro-organisms. On this point, how- 

 ever, Duclaux was unable to afford any certain proof. Later workers attempted 

 to .arrive by various ways at a solution of this highly important matter, and 

 mostly by endeavouring to ascertain whether the ripening of cheese could be 

 accomplished in the absence of any fermentative organisms. F. SCHAFFER and 

 ST. BONDZYNSKI (I.) showed that curd prepared from boiled milk does not ripen ; 

 and, according to FREUDENREICH (III.), the same applies equally to Pasteurised 

 milk. Moreover, L. ADAMETZ (VI.) found that neither does ripening occur 

 when bactericidal substances, such as thymol or creoline, are added to the fresh 

 curd; and the same result was attained by L. PAMMEL (I.) by the use of 

 hydrogen peroxide. 



177. Changes in the Bacterial Flora of Ripening Cheese. 



L. Adametz also attempted to ascertain the active cause of the ripening 

 process in a new way, namely, by tracing the quantitative and qualitative 

 alterations occurring in the bacterial content of the ripening curd. These 

 researches made on a Sornthal (Switzerland) soft " household " cheese, in 

 addition to Emmenthal cheese led to the following results: 



(i) The freshly precipitated curd, moulded in the press and freed from 

 excess of whey, contains between 90,000 and 140,000 bacteria per i gram, a 

 comparatively large number of these being able to liquefy gelatin, and conse- 

 quently excreting a peptic ferment. 



