2o6 ECONOMIC BACTERIA IN MILK AND MILK PRODUCTS 



of them. They do not form spores. Nor will they grow in the 

 presence of 2 per cent, acid. Most of them occur in tvinter 

 milk, but the temperature does not favour their increase.^ In 

 ordinary sound curd there is lactose present, which in due time 

 is decomposed by various organisms involved in ripening. In 

 some degree we get lactic acid produced ; but we also get gas 

 liberated, and in consequence smaller or larger holes are pro- 

 duced. Occasionally this process takes place in an extreme 

 degree, and the whole cheese becomes swollen and inflated. Such 

 cheese is termed "spongy," or " puffy," or " blown." It has been 

 found that some 25 species of bacteria have the power of producing 

 this abnormality, and on occasion it may be so marked as wholly 

 to ruin the cheese. Freudenreich found three species of organism, 

 which he termed Bacillus Guillebeau, a, b, and c, which produced 

 inflated cheese when inoculated into fresh curd. Bad flavour was 

 also present. In the holes produced by B. Guillebeau, a, CO., and 

 gases were found in some abundance. B. coli communis (Lloyd), 

 B. lactis aerogenes^ and B. ScJiafferi have also been isolated from 

 such inflated cheese. Adametz also separated an organism termed 

 Micrococcus SorntJialii from a Sornthal dairy which was able to 

 produce gassy cheese. Baumann believed that this abnormality 

 was due to organisms ordinarily capable of producing normal 

 pitting in cheese, but which if present in excessive numbers 

 brought about the abnormal pitting. He isolated B. diatrypeticus 

 casei, a facultative anaerobe, non-motile, and a liberator of COg and 

 H in substances containing sugar, with the formation of alcohol 

 and lactic acid. As a matter of fact, there is evidence to show 

 that it is not the exclusive property of one or two organisms to 

 inflate cheese. Gas-producing bacteria in large numbers in milk 

 are capable of doing this, and the abnormality is widespread. It 

 may be prevented by not using milk containing gas-producing 

 bacteria,^ or by the addition of 3 per cent, of sodium chloride, or 

 acid, to the freshly precipitated curd, or by obtaining milk from 

 perfectly healthy udders and keeping it free from all dust and 

 uncleanness. There is evidence to show that bacteria from sore 

 teats, or dirty water, or dust and manure, may set up spongy 

 •cheese. Lloyd states that when a cheese shows signs of spongi- 

 ness it is well to take special precautions to ensure obtaining 



^ Twelfth Annual Report of Agricultural Expt. Sta., Wisconsin, 1895. 



2 These organisms can be detected by the fermentation test, or by placing 

 suspected milk in flasks at 90° F., when gas-producing bacteria, if present, will 

 make themselves obvious. 



