THE ADVANTAGES OF A CARBOHYDRATE MEDIUM 



IN THE ROUTINE BACTERIAL EXAMINATION 



OF MILK 



JAMES M. SHERMAN 



From the Bacteriological Laboratories of the Pennsylvania State College and 

 Agricultural Experiment Station 



INTRODUCTION 



The object of this paper is to direct the attention of labora- 

 tory workers to the advantages over plain agar of an agar con- 

 taining a fermentable carbohydrate, for use in the bacteriological 

 control of market milk. Some laboratories are probably aware 

 of these facts, but since the standard methods for the bacterial 

 analysis of milk prepared by the committee of the American 

 Public Health Association^ call for the use of plain agar, and since 

 this medium is used in many of the largest laboratories making 

 routine analyses at the present time,^ it seems pertinent to sub- 

 mit a few data on these points. 



METHODS 



The bacterial counts reported herein were made on plain agar 

 prepared according to the standard formula, and on lactose agar 

 with the same ingredients plus 1 per cent of lactose. Liebig's 

 beef extract and Witte's peptone were used. The media were 

 adjusted to a reaction of 0.5 per cent normal acid to phenol- 

 phthalein, which reaction is, according to the results obtained in 

 this laboratory,^ better than a higher acidity. 



In the determination of bacterial num.bers triplicate plates 

 were made of each dilution, and the counts were made after 



1 Meetings of Am. Pub. Health Assn., Rochester, N. Y., September, 1915. 

 ' U. S. Pub. Health Service, Public Health Reports, 30 : 2349-2394. 

 •'Penn. Agr. Expt. Sta., Report for 1914-1915. 



481 



