CHAPTER II. 
MILK SECRETION. 
The Mammary Gland as a Secretory Organ.— The mam- 
mary gland of females belonging to the order of mammalia, 
secretes a fluid known as milk. This substance is strictly a 
secretory product. There are two kinds of glands present 
in the animal body; viz., the excretory and the secretory. Gen- 
erally speaking, an excretory gland is one which receives or 
absorbs the waste matter of the body, and causes it to be 
carried off without causing any marked change to take place 
in the substance excreted. A secretory gland is one in which 
the raw material is obtained from the blood and then manu- 
factured into a special different product within the gland 
itself. As an example of a secretory gland, the milk-gland 
of the cow’s udder is an apt illustration. The glands in the 
mouth secreting saliva, and those in the walls of the stomach 
secreting the digestive fluids, are also secretory glands. 
Internal Structure of Cow’s Udder. — The cow’s udder is 
composed of two separate glands, the right and left halves. 
These two glands are distinctly separated from each other 
by a fibrous tissue running longitudinally. This fibrous par- 
tition extends along the abdomen in front, and back to a point 
between the thighs of the cow. It also serves to hold the 
-cow’s udder in place. ‘There is no connection at all between 
the right and left gland, and consequently milk cannot be 
‘drawn from the left side over to the right, and vice versa. 
Each of these right and left halves is again divided into 
two parts, thus making the cow’s udder appear in quarters. 
The cow’s udder may then be said to consist of two glands 
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