106 ABSTRACTS 



Counts made from the cream and sediment of both iced and preserva- 

 tive samples showed that this concentration of the bacteria in the cream 

 and in the sediment occurred in all of the samples. Where no cream 

 was present as in skim milk, the bacteria did not rise to the surface but 

 sedimented in large numbers showing that the reason for their con- 

 centration in the cream was because they were buoyed up on the fat 

 drops. In the samples studied, there was a strong tendency for the 

 larger clumps of bacteria to concentrate in the cream, the bacterial 

 groups which occurred in the sediment rarely consisting of more than two 

 individuals. 



The Pasteurization of Dairy By-products. Robert S. Breed and 



W. D. DOTTERRER. 



In some work done for the New York State Commission for the 

 Investigation of Bovine Tuberculosis during the summer and fall of 

 1915 on the pasteurization of whey, it has been found that whey, 

 heated between 140 and 180°F. and allowed to cool slowly in the whey 

 tank, sours with an almost pure lactic acid fermentation due to lactic 

 acid bacilli belonging to the Bacillus bulgancus group. Immediately 

 after heating the numbers of bacteria in the raw whey are reduced from 

 millions to tens of thousands per cubic centimeter. During the 18 to 

 20 hour period which elapses before the whey is returned to the farmers 

 and during which time it is cooling slowly, there is a rapid growth of the 

 lactic acid bacilli which have survived the heating so that the whey 

 contains from tens to hundreds of millions of these organisms per cubic 

 centimeter as delivered to the farmers. The other types of bacteria 

 present (largely spore forming bacilli) do not increase in number to 

 any marked extent. The acidity of the whey as delivered to the far- 

 mers was found to varj^ from 0.3 to 0.4 per cent calculated as lactic acid. 



On the other hand the unheated whey which was examined showed 

 an acidity of 1.2 per cent and contained several million miscellaneous 

 bacteria, one and a half billion lactic acid bacilli and about thirty 

 million yeasts per cubic centimeter. Neither of the latter developed 

 on the agar media and would not have been found if the micro- 

 scopic method of counting had not been used. No heated whey was 

 found which contained yeasts, a condition which suggested that the 

 improvement in the quality of cheese frequently noted where pasteuri- 

 zation has been adopted has arisen from the elimination of yeasts from 

 the whey tank and so from the farmers' milk cans. 



On two successive days at one of the factories, the predominant 

 lactic acid organism in the making vat was found to be a bacillus 

 instead of the more common Streptococcus. 



The Effect of Air Pressure on Potable Waters During Stora^ge. W. D. 



Frost and Freda M. Bachmann. 



Steel pressure tanks are in common use for storing water. The 

 question is raised whether or not the effect of the air under pressure 

 in these tanks could be injurious to the contained bacteria, or, in other 



