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 stricth" 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 bod}-, and causes it to be carried oft" 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 dift'erent 

 product within the gland itself. As an example of a secretory 

 gland, the milk-gland of the cow's udder is an apt illustrati(m. 

 The glands in the mouth secreting saliva, and those in the walls of 

 the stomach secreting the digestive fluids, are also secretor}- 

 glands. 



Internal Structure of Cow's Udder. — The cow's udder is 

 composed of two separate glands, the right and left ha]\x-s. 

 These two glands are distinctly separated from each other hy a 

 fibrous tissue running longitudinaUy. This fibrous partition 

 extends along the abdomen in front, and back to a point between 

 the thighs of the cow. It also ser^•es 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 xict 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 ma}' 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; 



