36 PRACTICAL DAIRY BACTERIOLOGY 



The production of gas is the cause of the ruin of vast quantities 

 of cheese. If milk contains a considerable quantity of this 

 bacterium, instead of the more common non-gas-producing 

 type, when it is made into cheese, the bacteria grow and de- 

 velop gas, the cheese becomes filled with the bubbles, swelling 

 more and more, until it finally results in what is known as 

 swelled cheese. At the same time that this swelling occurs, the 

 flavor of the cheese becomes unsatisfactory, so that the swelled 

 cheese is practically worthless, at least in a case of extreme 

 swelling. These organisms have been the cause of the loss of 

 enormous amounts of money on the part of cheese makers. In 

 butter making they are not so disastrous, but here, too, their 

 presence is undesirable, for they sometimes produce unpleasant 

 flavors in the creams, resulting in an inferior grade of butter. 

 This type of organism, therefore, is decidedly the dairyman's 

 foe. 



Varieties of Gas-producing Bacteria. Bad. aerogenes has 

 been mentioned above as a single type, but there is a long list 

 of bacteria capable of developing acid-producing gas, and grow- 

 ing, generally, much like the one which we have described. 1 These 

 have been separated into several groups, with several names. 

 The dairyman cannot expect to separate the different types 

 from each other, and it is not appropriate in this work to at- 

 tempt to describe them. They may all be considered together, 

 therefore, as the type of gas-producing Bad. lactis aerogenes. 

 One special type, however, which in most respects agrees with 

 the one described above, must be specially noticed. This one 

 also produces acid and gas from milk in the same method as 

 the Bad. aerogenes, and its growth on potato, agar and else- 

 where agrees in almost all respects with it. But it is found to 

 be motile, and covered with a number of flagella. It is, there- 

 fore, not a Bacterium, but a Bacillus. The organism in ques- 



i Harrison. Cent. f. Bact. II., xiv., p. 359, 1905. 

 Conn. Ann. Rep. Storrs. Exper. Sta., 1906. 



