CHAPTER XV. 



MILK: ITS ORIGIN AND COMPOSITION. 



i. Secretion of Milk. The milk of animals is a 

 peculiar secretion manufactured in special glands known 

 as mammae. The udder of the cow con- 

 sists of such glands, with which are 

 associated four teats. Each teat has a 

 small single orifice through which the 

 milk escapes when pressure is put upon 

 it as in the act of suckling or milking. 

 Just inside the orifice of the teat and for 

 some distance inwards is an open cavity, 

 the lactiferous sinus or " milk-cistern," in 

 which .the secretion is stored when the 

 animal is " in milk." From the reservoir 

 there branch off into the substance of the 

 udder a series of tubular channels or 

 lactiferous ducts, irregular in diameter and 

 distribution, but becoming smaller and 

 smaller as they are traced backwards. 



FIG. 38. Diagram il- 11 r u- L It. 



lustrating origin of The finest branches, of which there 



milk in udder of cow. 11. 



a Alveoli in which are thousands, ultimately end m exceed- 



secretion takes place; . 



b lactiferous duct; mgly small pouch-like structures termed 



c orifice of teat. 7 T . 



alveoli (Fig. 38). It is in these that 



the actual 

 alveolus is 



consists of 



232 



manufacture of milk takes 

 about ^J n of an inch in 

 a hollow cavity lined with 



place. Each 

 diameter and 

 a single layer 



