MARSHALL ON THE AiitlATION OF MILK. 191 



tarding influence upon the growth of micro-organisms, as exercised by 

 anaerobic conditions is conx'erned, I do not believe it can be taken into 

 consideration, for the ditlerence in time would be too short to have any 

 relative importance. 



There is, however, the matter of lactic acid fermentation to consider 

 relevant to this theme, for upon it is dependent much of value in the 

 handling of milk. The importance of lactic acid starters in controlling 

 "oflf-fermeutations" in milk cannot be treated more advantageously than 

 here where so many fermentations are possible. It is a well known fact 

 that the earlier the lactic acid bacteria are added, the better are the re- 

 sults. This of course falls logically and naturally in the line of bacterio- 

 logical deductions. Hence if any set of conditions can be made to favor 

 this class of micro-organisms, greater safety is assured in the kind of 

 fermentation which milk is likely to undergo. In our experiments we 

 have been led to the conclusion that, with few exceptions, the lactic acid 

 group of bacteria is favored by an abundant supply of oxygen. By the 

 aeration of milk, therefore, wo are furnishing these conditions which 

 incite the fermentation sought. 



From the standpoint of pure milk supply, we can say that aeration 

 favors an interchange of gases in milk with those of the surrounding 

 atmosphere thereby tending to eliminate any gaseous odors or taints ; it 

 also favors lactic acid fermentation under ordinary conditions thus con- 

 trolling other obnoxious and perhaps injurious fermentations. To the 

 producers it indicates how easily the gases of the stable are incorporated 

 in the milk and what any agitation of the milk in the stable may lead to 

 and how desirable it is to keep milk in an absolutely pure atmosphere. It 

 further warns him that in closing up a can of warm unaerated milk there 

 is always great danger of greater or less anaerobic fermentation setting 

 in and causing trouble in one way or another. 



