28 Milk and Its Products 



period of lactation progresses. The hardening of 

 the fat and the shrinking in the size of the glob- 

 ules are also more marked when the animal again 

 becomes pregnant. In the case of cows that are 

 milked for a prolonged period, as sometimes hap- 

 pens with farrow and spayed cows, the milk often 

 becomes abnormally rich, not only in fat, but in 

 casein ; and in such cases the fat is usually made 

 up of very minute globules. 



It is usually observed that milks drawn at 

 night and morning differ quite widely in the per- 

 centage of fat. This is not because there is any 

 difference in the milk secreted by night or by day, 

 although when cows lie still there is a larger per- 

 centage of water and a correspondingly less per- 

 centage of solids in the milk. The difference in 

 the milk drawn at morning and evening is due to 

 the unequal time that elapses between the periods. 

 In general, the milk is richest in fat that is drawn 

 after the shortest period, and this has been shown 

 to be the case where cows have been milked three 

 or four and even five times per day. It is, 

 however, not an invariable rule that the milk is 

 richest succeeding the shortest period. Not infre- 

 quently it has been found that the milk is richer 

 after the longer period. In a series of observa- 

 tions made by the writer upon 12 cows, ex- 

 tending over 221 days, in 72 cases the percentage 

 of fat was greater in -the morning ; in 114 cases 

 it was greater in the evening, and in 35 cases 

 there was a difference of .1 of 1 per cent or less 



