186 Dairy Bacteriology. 



rious sources, such as a lack of aeration, improper feeding, 

 retention of animal gases, etc., but in all these cases it was 

 nothing more than a surmise. Very often the milk does 

 not betray any visible symptom of fermentation when re- 

 ceived, and the trouble is not to be recognized until the 

 process of cheese-making is well advanced. 



Studies from a biological standpoint have, however t 

 thrown much light on this troublesome problem; and it 

 is now known that the formation of gas, either in the 

 curd or after it has been put to press, is due entirely 

 to the breaking down of certain elements, such as the 

 sugar of milk, due to the influence of various living germs. 

 This trouble is, then, a type fermentation, and is, therefore, 

 much more widely distributed than it would be if it was 

 caused by a single specific organism. These gas-produc- 

 ing organisms are to be found, sparingly at least, in al- 

 most all milks, but are normally held in check by the 

 ordinary lactic species. Among them are a large number 

 of the bacteria, although yeasts and allied germs are often 

 present and are likewise able to set up fermentative changes 

 of this sort. In these cases the milk-sugar is decomposed 

 in such a way as to give off CO 9 and H, and in some cases r 

 alcohol. 



According to Guillebeau, a close relation exists between 

 those germs that are able to produce an infectious inflam- 

 mation (mastitis) in the udder of the cow and some forms 

 capable of gas evolution. Several outbreaks of " gassy " 

 milk have been traced directly to animals suffering from 

 an acute udder inflammation in which it has been shown 

 that the organisms producing this disease were the direct 

 cause of the gas production in the milk. 



If pure cultures of these gas-producing bacteria are added 



