MISCELLANEOUS LACTIC BACTERIA. . 7 1 



years, the organisms of the first group are the chief milk- 

 souring organisms, while those belonging to this group are 

 of secondary importance. In many samples -of sour milk 

 these aerobic bacteria are present in small numbers, perhaps 

 2% to 5% of the total, whereas the organisms of the first 

 group will comprise 90% of the total. Moreover, the species 

 of this group do not multiply very readily in the milk in the 

 presence of those of the first group. All these facts together 

 indicate that they are secondary factors in ordinary milk 

 souring, although occasionally they alone are concerned. 



The fact, however, that they produce gas in abundance 

 makes the type of much importance in certain dairy prob- 

 lems. Sour milk very frequently contains bubbles of gas, 

 and when this occurs it must probably be attributed to the 

 fact that some species of this type of lactic organisms are 

 present. The production of a large amount of gas is the 

 cause of one of the most troublesome " faults " which appear 

 in the ripening of cheese, and it is this group of organisms 

 primarily that are concerned in the process. While these 

 gas-producing, aerobic bacteria, therefore, are commonly not 

 the chief organisms concerned in souring of milk, they do 

 have considerable importance in other dairy phenomena. 



Other Lactic Types. In addition to these two primary 

 forms of lactic bacteria quite a number of others have been 

 found in greater or less abundance. These may also be 

 divided into a few types, but their importance in dairy prob- 

 lems is probably insignificant compared to that of those 

 already referred to. Only brief mention is, therefore, needed. 



A Liquefying Type. This type of lactic organism has the 

 power of producing an enzyme ferment, as will be explained 

 in the next group of bacteria, and, as a result, after curdling 

 the milk the curd is subsequently slowly dissolved. The 

 organisms here classed belong, therefore, to the next type 

 of bacteria as well as to the lactic type. They are rather 

 common in milk and sometimes appear to be cocci and some- 



