64 Dairy Bacteriology. 



it is now believed that these organisms find more favor- 

 able growth not so much on account of the lactic acid 

 formed as in the absence of dissolved oxygen in the milk 

 which is consumed by the sour milk organisms. 



Most of the butyric class of bacteria are spore-bearing, 

 and hence, they are frequently found in boiled or steril- 

 ized milk . The by-products formed in this series of changes 

 are quite numerous. In most cases, butyric acid is 

 prominent, but in addition to this, other organic acids as 

 lactic, succinic, and acetic are produced, likewise different 

 alcohols. Concerning the chemical origin of butyric 

 acid there is yet some doubt. Duclaux 1 affirms that the 

 fat, sugar, and casein are all decomposed by various forms. 

 In some cases, the reaction of the milk is alkaline, with 

 other species it may be neutral or acid. This type of 

 fermentation has not yet received the study it deserves. 



In milk these organisms are not of great importance, 

 as this fermentation does not readily gain the ascendency 

 over the lactic bacteria. It has been supposed until re- 

 cently, that the rancidity of butter was attributable to 

 the action of these ferments, but the general belief now 

 is that this is a purely chemical change that may be in- 

 fluenced but not caused by these organisms. 2 



63. Bitter milk. A bitter taste may be imparted to 

 milk in a variety of ways. In some cases it is due to 

 improper feeding caused by eating herbs such as lupines, 

 wormwood, or chicory. Then again, at certain periods 

 of lactation, a bitter salty taste is occasionally noted in 

 the milk that is peculiar to individual animals. 



A considerable number of cases of bitter milk have, 

 however, been traced to bacterial origin. For a number 

 of years the bitter fermentation of milk was thought to 



1 Duclaux, Principes de Laiterie, p. 67. 



2 Duclaux, Compt. rendu, 102: 1077. 



