COMPOSITION AND QUALITIES OF MILK 295 



this muscle is weak and does not close the opening tightly; 

 then the milk leaks out. Sometimes it is very strong and does 

 not let the milk out easily; the cow is then "hard" to milk. 

 The cow has some control over the sphincter muscles which 

 guard the openings from the milk cisterns and can "hold up" 

 her milk. She does so usually only when scared or angry. 

 A feed at the time of milking will cause her to forget her 

 excitement. Excitement also hinders the secretion of milk 

 in the glands. Kindness and quietness should always be ob- 

 served in handling milch cows. 



Milk contains all the food elements necessary for the 

 growth and development of young animals. In America the 

 milk from the cow is the only milk that is used for human 

 food, but in some countries the milk from the ass, mare, 

 goat and ewe are also used. Cow's milk does not have a 

 fixed composition. There are several things that affect it. 

 Of these we shall speak in another paragraph. The com- 

 ponent parts of milk may be grouped as follows: 1. Water. 

 2. Albuminoids, namely, casein and albumen. 3. Fats. 

 4. Sugar. 5. Ash. The last four items are called milk soU 

 ids. They may be arranged in outline as follows: 



''Water 87.5% 



/Ash.. 7% 



Milk{ Sugar 4.7% 



Solids 12.5%, I Albumen 5% 



Casein 2.8% 



^Fat 3.8% 



The specific gravity of cow's milk is usually taken at 1.032. 



A study of the composition of the milk from the several 

 kinds of animals shows that they vary a great deal, but all 



