Part II.] PASTEURIZATION OF MARKET MILK. 107 



The reason for this lies in the well-known fact that heat 

 destroys the viscosity of the milk. It makes milk more fluid. 

 The greater fluidity gives the fat globules greater freedom of 

 motion. They encounter less resistance in their upward pas- 

 sage, and, true to the law of gravity, they promptly rise to, the 

 surface, forming the cream line. The reason why, at higher 

 temperatures, — those above 145.4° F., — the cream line fails 

 to form rapidly, and possibly entirely disappears, must be 

 attributed to the fact that at temperatures above 145.4° F. the 

 albumen begins to coagulate abundantly, and this coagulation, 

 though invisible to the naked eye, hinders, or entirely blocks, 

 the upward passage of the fat globules. They do not come to 

 the top and the cream line does not form. 



In order to preserve the cream line, therefore, the milk should 

 be heated not to exceed 145° F., and the temperature of the 

 heating medium should be but a few degrees higher, otherwise 

 the milk that comes in direct contact with the heating surface 

 may be exposed to heat sufficiently high to damage the cream 

 line. 



There are other more or less incidental factors which in- 

 fluence the cream line, such as the nature and amount of 

 agitation to which the milk is subjected, the nature and age 

 of the milk, the period of lactation, etc.; but these are local 

 details, and can be taken care of locally in the case of each 

 individual plant. 



With a clear understanding of these simple facts and princi- 

 ples, therefore, it is obvious that the proper pasteurization of 

 market milk does not destroy nor retard the cream line, but 

 that its formation maj^ actually be enhanced by it. 



Summing up, then, it is reasonable to state that proper care 

 in the handling and production of milk minimizes danger of 

 infection, but that no amount of care can insure the public 

 against infection of the cleanest milk from unrecognized carriers 

 of disease. While milk from private dairies, kept under most 

 ideal conditions, often does surpass in quality, though not 

 necessarily in safety, milk from the average pasteurizing plant, 

 the pasteurizing plant furnishes a far safer product than the 

 average private dairy and milk peddler. 



Pasteurization, properly executed, is an efficient and practical 



