3*4 



MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



has been produced. There are differences not only in the numbers of 

 organisms but also in the species which may be found in different samples 

 of fresh milk. Both of these factors are important in the later changes 

 which may take place. The effect of numerical initial contamination 

 may be seen in the following tables where milk starting out with different 

 numbers of organisms was kept under similar conditions until coagulation. 

 Plate cultures made from these three samples show the relative develop- 

 ment of the number of organisms. 



Effect of Initial Contamination on Development of Bacteria and Keeping Quality of Milk. 

 Milk Having Moderately High Initial Contamination. 



Milk Having Moderate Initial Contamination. 



Bacteria per c.c. in fresh milk Bacteria 12 hours Bacteria 36 hours Hours to curdling 



3,000 



14,000 



I 49, 6 5; 00 



99 



Milk Having Small Initial Contamination. 



Bacteria per c.c. in fresh milk 



Bacteria 12 hours 



Bacteria 36 hours 



Hours to curdling 



3 2 5 



i,7 12 . 



10,125,000 



121 



These samples were all kept at a constant temperature of 21 

 and the difference in the curdling time can therefore be fairly attributed 

 to the difference in the initial contamination of the three samples. 

 All three of the samples showed a normal development of the lactic 



