THE RELATION OF MICROORGANISMS TO MILK 



387 



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 development of the number of 

 organisms. 



These samples were all kept at a constant temperature of 21° and 

 the difference in the numbers of bacteria and the curdling time can 

 therefore be fairly attributed to the difference in the initial contamina- 

 tion of the three samples. All three of the samples showed a normal 

 development of the lactic organisms, which constituted over 99 per 

 cent of the total organisms present at the time of curdling. While 

 this may be considered as showing the normal effect of the original 

 contamination upon the milk, it is well to bear in mind the fact that 

 there are many apparent exceptions due to some particular type of 

 organism predominating and interfering with the normal development " 

 of the lactic types. 



Straiotng. — ^The straining of milk is one of the most common 

 operations in connection with its handhng and is considered by most 

 dairymen as one of the most essential from the standpoint of the qual- 

 ity of the milk. If milk is strained through cheese cloth or wire 

 gauze much of the insoluble dirt can be removed. This has led to the 

 general belief that straining improves the sanitary and keeping quali- 

 ties of the milk. 



The effect of straining on removal of insoluble dirt is shown by 

 the following results of the tests: 



Diet Removed by Passing Milk through Two Thicknesses of Fine Cloth 

 (Weight of insoluble dirt given in milligrams per liter of milk) 



It may be noticed that even after straining the milk contained 

 appreciable quantities of insoluble dirt which had passed through 

 the strainer cloth. The difference in per cent of dirt removed in 



