423 



the young animal. But casein takes the place of the 

 fibrin of the blood, and fat is also found in milk, in 

 much larger proportion. This fluid also contains sugar ? 

 which is peculiar in its character and has therefore 

 received the name of sugar of milk. Butter is pro- 

 duced by the coalescence of the small particles of oil 

 which are suspended in milk, and partially separated in 

 the cream. Chemically considered, it is a mixture of 

 oleine and margarine. On partially cooling melted 

 butter, the latter collects at the bottom of the liquid 

 oleine, which forms the other constituent ; a portion 

 at the same time remains in solution. Beside the 

 above substance, butter contains phosphates and other 

 salts, with certain neutral fats, from which it derives 

 its flavor. 



1052. CHEESE. On exposure to the air 



Why is the . . , 



curd separated for a considerable time, the sugar contained 

 by exposure? ^ R m jjj . - g p art i a iiy converted in lactic acid, 



and the casein is precipitated. One reason of this pre- 

 cipitation is to be found in the neutralization of the 

 free alkali of the milk. The casein having thus lost 

 its solvent, assumes the solid form. The coagulation 

 of milk may also be effected by rennet, which con- 

 sists of an infusion of the lining membrane of the 

 stomach of the calf. Its mode of action is not well 

 understood. 



1053. SOLID MILK. Milk may be 

 brought into the solid form by careful 

 pared? evaporation, with a moderate heat. It 



must be constantly stirred during the process. A ma- 

 chine has been recently patented which secures all of 



