266 AGRICULTURAL BACTERIOLOGY. 



bubbles of gas. This gas can be collected, if desired, in a 

 properly devised vessel, and measured. If it is found that the 

 amount of gas is considerable, the milk from which the sample 

 was taken must be rejected, since its use in cheese-making 

 will be pretty sure to produce an undue amount of gas, with 

 the accompanying inflation of the cheese, which it is desired 

 to avoid. This fermentation test is in practical use in certain 

 cheese factories and proves to be of considerable value. It is 

 to be remembered that the normal lactic bacteria produce no 

 gas, and do not therefore give rise to this trouble. The use 

 of pure cultures of common lactic bacteria to inoculate the milk 

 in cheese-making, is of value in correcting this trouble and is 

 strongly recommended by some bacteriologists. 



There are quite a number of other types of abnormal ripen- 

 ing known to be caused by the growth of unusual microor- 

 ganisms. Cheese sometimes develops such a bitter taste as to 

 be practically worthless. The fact that bacteria can produce 

 a bitter taste in milk suggests that they may be the cause of 

 this trouble in cheese. Only one case of such bitter cheese 

 has been investigated by bacteriologists, and this was found to 

 be caused by a definite species of bacterium, closely allied to 

 one previously found to be the cause of a dairy infection of 

 bitter milk. It is a coccus form, named by Freudenreich, M. 

 casci ainari. The organism not only produces a very bitter 

 taste in milk in the course of two days, but, if it is inoculated 

 into milk which is subsequently made into cheese, the cheese 

 acquires the bitter taste during the ripening, thus demonstrat- 

 ing the causal connection between this organism and the bitter 

 cheese trouble. 



One of the common faults in the ripening of cheeses is a 

 putrefaction of the product. This is more likely to occur in 

 the soft cheeses than in the hard cheeses, doubtless because 

 of their larger amount of water. Indeed the soft, moist cheese, 

 with its high proteid content, is a most excellent medium for 



