4 i2 HUMAN PHYSIOLOGY 



the fat of the milk, and is therefore white. From the curd 

 a colourless whey containing albumin and milk sugar exudes. 



Fats. Olein is the chief fat, but fats of the lower fatty 

 acids are also present. They exist in a fine state of sub- 

 division, suspended in the milk plasma, and each globule is 

 apparently surrounded by a thin covering of proteid, which 

 has to be removed by the action of an acid or an alkali before 

 the fat can be extracted with ether. 



Sugar. The disaccharid lactose is the sugar of milk 

 (see p. 317). Under the action of various micro-organisms 

 it is split up to form lactic acid, thus causing the souring of 

 milk. 



Phosphorus Compounds. In addition to caseinogen, milk 

 contains other organic phosphorous compounds. Among 

 these is lecithin and a compound which has been called 

 phosphocarnic acid, the constitution of which is not fully 

 understood. In human milk the greater part of the 

 phosphorus is in organic combinations, while in cow's milk 

 the amount in inorganic compounds is much greater. 



Milk is specially rich in calcium and potassium, but the 

 amount of iron in milk is very small, and therefore, when 

 the child has used up the store of iron which it has in its 

 body at birth, it is necessary to replace the milk-diet l>y 

 foods containing more iron. 



