54 MILK [v 



leads to the changes in the properties of milk so 

 familiar to all. In this Chapter we shall only casu- 

 ally refer to the micro-organisms which effect these 

 changes, and shall leave a more full treatment of 

 this important subject to a following Chapter. 



Creaming of Milk. Milk, as it comes from the 

 udder, may be described as of practically uniform 

 composition. If, however, we let it stand at rest for 

 some time, we find that the uniformity of its com- 

 position is disturbed by an accumulation, which 

 takes place more or less quickly on its surface, of 

 its minute fatty globules. Concurrently with this 

 separation of the fat, a change in the colour of the 

 main body of the milk will be observed. By the 

 removal of the fat the opacity of the milk is 

 diminished, and it is rendered more transparent. 

 This has the effect of imparting the bluish tinge, 

 so characteristic of skim milk. The surface layer 

 of milk, which is thus enriched in fat, is known as 

 cream. Now there is a popular belief to the effect- 

 that the richness of milk in fat is indicated by the 

 depth of this cream layer ; and while, no doubt, this 

 is true, within certain limits, it is, as we shall im- 

 mediately proceed to show, not necessarily so. The 

 tendency which the milk globules possess to rise to 

 the top exists to such an extent that if a quantity of 

 milk six inches deep be allowed to stand undis- 

 turbed, at a temperature of 15 C. (60 Fahr.), for 





