130 STATE BOARD OF AGRICULTURE. 



A STUDY OF THE DETEKMINATION OF BACTEEIA IN :\I1LK 

 IN RELATION TO THE COMPOSITION OF THE MEDIA.* 



BY Z. NOUTHHUl" AND BKLL FAURAM). 



Ill order to determine the media most favorable to the growth of 

 germs in milk, different lots of media were prepared to ascertain : 1. 

 the degree of acidity; 2, the percentage of lactose; 3, the percentage 

 of peptone, most conducive to the growth of the milk germs. 



For determining the degree of acidity, media were prepared, using 

 11/2% agar, 1% peptone and !/>% salt. The agar was digested 20 

 minutes in the autoclav at 120" C and added to the strained meat in- 

 fusion containing the peptone and salt. This was titrated to find 

 out the reaction and then divided into four portions, adjusting them to 

 5^, 10°, 15', 20^ acid respectively, with normal NaOH; counterpoised, 

 heated in flowing steam for 30 minutes, counterpoised again and each 

 portion titrated and the reaction readjusted. Boiled over freely and 

 this was then filtered, tubed (about 10 cc. in each tube), and sterilized 

 for three successive days in flowing steam. 



The dilution flasks were prepared as follows: 100 cc of a .06% salt 

 solution was put into 375 cc. Erlenmeyer flasks and sterilized 10 

 minutes in the autoclav at 120^ C. 



Each sample of milk was secured in sterile Erlenmeyer flasks, the 

 acidity determined and plates made as soon as reaching the labora- 

 tory. 



Milk from 0.0 hours old was used for plating. Samples IV to VI 

 and XIV to XX were taken directly from the ten gallon cans in the 

 milk room of tht^ dairy barn. The other sam])les were obtained at the 

 dairy or from outside sources. 



*This work has beeii'done at tlif, instigation of a "Committee on Standard Methods of Bacterial 

 Millc Analysis," of the American Public Health Association. " 



