10 



The presence of the proteus form in the cheese of July 29th, even though 

 it did not increase in numbers, likely accounts for the cheese of that day 

 going "off" in flavor. Such forms are favored by the warmer temperature 

 of the variable room; but the large numbers of the lactic acid bacteria pre- 

 vent their growth and soon destroy most of them. Gas-forming bacteria do 

 multiply and are found in large numbers in open cheese, and especially in 

 cheese in which this taint develops early. This may be due partly to a lack 

 of acid in the cheese, and partly to various other defects in the manufacture. 

 Both B. Coli and B. lactis aerogenes produce mottling. Conclusive evi- 

 dence of this fact was obtained from a number of our experiments, made by 

 using starters of these gas-producing organisms and manufacturing cheese 

 therefrom. The mottles were most marked at the places where the particles 

 of curd came together; holes and cracks also developed at these places, and 

 it was evident that the gas produced by these organisms, particularly the 

 hydrogen, had a marked bleaching action upon the curd. We also found that 

 the white particles produced by bleaching contained much larger numbers of 

 the gas-producing organism than other portions of the cheese. 



The results of more detailed experiments upon this phase of the question 

 will be given in a subsequent publication. 



The lactic acid bacteria decline most rapidly in cheese kept in a room with 

 a variable temperature; and when such decline takes place, any other bacterial 

 species present is likely to multiply and produce its characteristic effects. 

 This, iperhaps, accounts for cheese going "ofi" in flavor when they become 

 quite old; and such an undesirable result is much more likely to occur in 

 cheese irom a room of variable temperature than from cool or cold rooms, 

 regulated by any of the methods adopted for the purpose. It may also be 

 possible that abnormal flavors are produced by organisms which can grow 

 only after a certain decomposition effected by a previous organism, the first 

 furnishing a suitable food for the second. We do not yet know whether lactic 

 acid bacteria render cheese suitable or unsuitable for the growth of any other 

 species. The neutralization of the lime salts of the cheese by the generated 

 lactic acid may at times bring about a condition suitable for the development 

 of other bacteria which may be present in a dormant condition. The meta- 

 biotic phenomena in cheese certainly require further study. 



As cheese become older, the lactic acid bacteria gradually lose their power 

 of producing lactic acid when introduced into fresh milk. No morphological 

 change can be detected in these bacteria. Colony formation on culture media 

 remain quite characteristic. Lloyd has obtained similar results. He, how- 

 ever, thinks that lactic acid formation still goes on in the centre of the cheese; 

 but, in our opinion, these bacteria are simply persisting forms of the contained 

 bacteria. Reference to the tables shows that, on several occasions, we had 

 an apparent increase of bacteria in cheese, several weeks old, kept at a tem- 

 perature of 40 degrees Fah.; and we explain these results as due to the unequal 

 distribution of bacteria in the cheese; for, by a number of experiments, we 

 proved that there could be no increase of the lactic acid bacteria in milk kept 

 at 40 degrees Fah. Some of the experiments on this point may be referred to. 



