CHAPTER II 

 MILK SECRETION 



The Mammary Gland as a Secretory Organ. The mammary 

 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. Generally 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 manufactured 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 partition 

 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 

 glands, 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 to be divided into 

 quarters. The cow's udder may then be said to consist of two 

 glands, one on each side, and four " quarters," two to a gland. 

 The division between the two quarters of a gland is not complete; 



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