EXPERIMENT STATION BULLETINS. 



299 



There is only one conclusion to be drawn from the above tests, although there are 

 some results which do not fully accord: there is no difference existing between the 

 germicidal action of unexposed milk and milk exposed to the air. Thus as far as 

 the germicidal action is concerned we cannot consider that aeration favors it. 



XXX. DOES AERATION AS PRACTICED REDUCE THE NUMBER OF BACTERIA WHILE THE 



MILK IS FLOWING OVER THE AERATOR? 



We were not able to employ a common milk aerator for this work but resorted to 

 the use of glass, tin and copper sheets which we used for aerating purposes when 

 studying the action of aeration upon the gas-content. The same inclined surfaces were 

 employed and aeration was carried out in exactly the same way. The number of germs 

 before aeration was estimated; the milk was run over the inclined sterile surfaces of 

 the materials mentioned and then the number of germs estimated again. In the follow- 

 ing' table will be found detailed results: — 



TABLE XXVI. 



DOES AERATION AS PRACTICED REDUCE THE NUMBER OF BACTERIA SIMPLY WHILE 

 THE MILK IS FLOWING OVER THE AERATOR? 



*The number of bacteria found in 1 c. cm. 



If this method of aeration can be regarded as one simulating the methods in vogue 

 we are forced to conclude that the simple act of aeration does not reduce the number of 

 micro-organisms in the milk and that if any reduction occurs it must be due to some 

 indirect action which aeration must have upon the milk. 



XXXI. SUMMARY. 



I. Milk drawn from the udder of a cow contains a high percentage of carbon 

 dioxide and a low percentage of oxygen. The gas pumped from milk con- 

 tains on an average 81.49£$ of carbon dioxide and 2.42% of oxygen. 

 II. During the milking process the percentage of carbon dioxide contained in 

 the pumped gases from milk dropped to an average of 59.63ffc and the 

 oxygen increased to an average of 13.17- 



