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 eases 
it was greater in the evening, and in 35. cases 
there was a difference of .1 of 1 per cent or less 
