PHYSIOLOGY AND SECRETION OF MILK 25 



contain the milk are broken down at each milking. 

 Every observer has noticed that a cow's udder will 

 fill one-third in the fifteen minutes prior to milking. 

 He has seen a pail filled with milk from an udder 

 which could have been placed in the pail, milk and 

 all, at the commencement of milking. How milk is 

 secreted is best expressed by an interrogation point. 

 The following substances in the indicated propor- 

 tions enter into the composition of average milk: 



Water 87.25 per cent. 



Fat 3.50 per cent. 



Casein 3.50 per cent. 



Albumen . .40 per cent. 



Milk sugar 4.60 per cent. 



Mineral substances 75 per cent. 



The variation of what is called pure milk from 

 different cows in full flow is as follows : 



Water 83.65 to 90.00 per cent. 



Fat 1.80 to 7.00 per cent. 



Casein 3.00 to 5.00 per cent. 



Albumen 30 to .52 per cent. 



Milk sugar 3.00 to 5.50 per cent. 



Mineral substances 70 to .80 per cent. 



In the matter of butter fat it makes a great differ- 

 ence to the owner whether his cow belongs to the 1.8 

 per cent, or to the 7 per cent, class. Cows well ad- 

 vanced in lactation often show a greater percentage 

 of solids than the above, but the quality of milk is 

 largely an individual characteristic, subject, however, 

 to marked changes of ill treatment or other causes. 

 Change of feed may control the quantity, but little 

 control of quality can be effected by the character of 

 the feed if fed under ordinary and normal condi- 



