DETERMINATION OF BACTERIA IN MILK 



585 



due, we believe, to a combination of the following factors: the 

 nitrogenous portions of the milk powder, the lactose, the buffer 

 content, and the use of washed agar. 



When 5 grams of skimmed-milk powder per liter of medium 

 is used, figuring on an average analysis of 50 samples of milk 

 powder, there is added about 0.25 per cent lactose and 0.17 per 



TABLE 4 

 The value of milk powder as a nutrient material 



EXTRACT AGAR, 



STANDARD METHODS 



A. P. H. A. 1916 



INFUSION AGAR, 



STANDARD METHODS 



A. P. H. A. 1910 



INCREASE 



OVER EXTRACT 



AGAR 



MILK-POWDER AND 

 WASHED AGAR. NO 

 OTHER INGREDIENTS 



INCREA8E 



OVER EXTRACT 



AGAR 



Raw milk 



Pasteurized milk 



cent protein (mostly casein). From results of the analysis of 

 skimmed-milk powder which were kindly supplied to us by Dr. 

 J. T. Kiester, of the Bureau of Chemistry, United States Depart- 

 ment of Agriculture, we have calculated the difference in per- 

 centage of lactose and protein if 5 grams of powder containing 

 the highest and lowest percentages found among 20 samples had 

 been used. 



