296 OUR HUMBLE HELPERS 



would avoid the risk of its turning. Suppose a few 

 drops of old milk or some remnants of any kind of 

 food are left in a pot, tucked away where they are 

 hard to get at: these impurities soon turn sour, es- 

 pecially in warm weather, and the milk, finding an 

 acid substance in the vessel, quickly spoils and 

 curdles. How often the milk itself is blamed for 

 this accident when want of cleanliness is the sole 

 cause ! 



"Milk contains three principal substances, 

 namely : cream, or fatty matter from which butter 

 is made; casein, or curds, used for making cheese; 

 and, finally, a substance with a slightly sweet taste 

 called sugar of milk. These three ingredients taken 

 away, hardly anything is left but water. To sepa- 

 rate these three, one proceeds as follows : 



"Left standing in a cool place and exposed to the 

 air, milk becomes covered, sooner or later, accord- 

 ing to the season, with a thick oily layer that takes 

 the name of cream; This is the material from which 

 butter is made. It rises to the surface unaided and 

 separates when simply exposed to the air. It is re- 

 moved with a skimmer. 



"What is left is skimmed milk, of the same white- 

 ness, the same appearance, as the original milk, but 

 deprived of its fatty matter. Into this skimmed 

 milk let us pour a few drops of some acid, lemon 

 juice for example. The milk turns and thick white 

 flakes are formed. Those flakes are the curd, the 

 casein, in short the material of which cheese is com- 

 posed. 



