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 increase 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 foetus. 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 scarcely 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- 

 creted. 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- 



