6 Milk and Its Products. 
the udder; a comparatively slight effort is all that is 
necessary to close the smaller vessels. Animals vary 
greatly both in the control they possess over these 
muscles and in their disposition to use it. Very few 
can completely close the larger ducts, and very many 
rarely exercise whatever power they do possess. Sud- 
den fright, the presence of strange persons or animals 
in the stable, any irregularity in the time or manner 
of feeding or milking, and slight feverish conditions, 
particularly sexual heat, are the most coiamon pro- 
vocatives to holding up milk. There are very many 
cows that contract the habit of holding up the milk 
upon the slightest provocation, and if the habit is 
once formed it is almost impossible to cure it, and 
the result is that the usefulness of the animal as 
a milk producer is largely destroyed, for the reten- 
tion of the milk in the udder interferes greatly 
with the activity of secretion, and in a short time 
permanently lessens it. 
The ultimate follicles.—The milk ducts, after 
branching and anastomosing in all directions, finally 
end in a group of small sac-like bodies known as 
acini, or ultimate follicles. It is in these small 
bodies that the secretion of the milk takes places. 
They are about 1-30th of an inch in diameter, and 
are found in groups of three to five, with a com- 
mon outlet at the end of each branching duct. 
In form and appearance they present marked 
changes according to the condition of the animal. 
During active lactation they are found in their 
highest development. When lactation ceases, the 
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