12 Milk and Its Products 
or ten months. But in this respect the individ- 
uality of the animal plays an important part, so 
that wide variations are seen in different individ- 
uals under the same conditions of food and care. 
After a shrinkage in the flow has once taken place, 
it is extremely difficult to again inerease it by 
increased food until after another calving. 
Effect of succeeding pregnancy.—The effect of the 
animal again becoming pregnant is to decrease the 
flow of milk. The cause of this decrease seems, 
in many cases, to be two-fold: First, a sympa- 
thetic effect, following immediately upon conception, 
and secondly, a shrinkage due to a turning away of 
a part of the blood from the udder to nourish the 
growing fetus. This shrinkage does not become 
marked until the fourth or fifth month of preg- 
nancy. In this respect, as in their power to “hold 
out,” individual animals show the widest variation. 
With very many the effect of becoming again preg- 
nant is so slight as to be searcely noticeable; with 
others it is so great as to materially interfere with 
the usefulness of the animal. 
Incomplete removal of milk.—One of the most 
important means of checking the secretion of milk 
lies in the incomplete removal of milk already se- 
ereted. We have already seen that the removal 
of the saline fluid from the ducts of the inactive 
gland is an efficient stimulus to secretion. So, too, 
the presence of milk in the ducts acts as a check 
to further secretion. Further than that, it not 
only checks secretion but is an actual irritant, suffi- 
