THE SECRETING GLANDS 293 



a responsive organ in this case the cells of the secre- 

 tory organ or gland). 



The active discharge of the secretion from the 

 cells is interrupted by periods of rest, during which 

 time, if they be examined under the microscope, after 

 the absorption of lymph, they will show accumula- 

 tions within themselves of their characteristic prod- 

 ucts as globules of mucin granules which are the 

 basic formation of the digestive ferments or enzymes, 

 granules of glycogen, globules of fat, sugar, and 

 protein, as in the case of the mammary gland. 



Excretion is a process similiar to secretion, the only 

 difference being that the fluids removed are the 

 waste products from the cells formed as a result of 

 metabolism. 



The Mammary Glands. These are accessory to 

 the reproductive system and secrete the milk. They 

 are two rounded eminences, one on each side of the 

 thorax, between the sternum and axilla and the 

 third and seventh ribs. Just below the centre is a 

 conical eminence, the nipple, which is dark, and is 

 surrounded by a pinkish areola which darkens in 

 pregnancy. It presents the orifices of the lactiferous 

 ducts, and consists of vessels mixed in with plain 

 muscular fibers,, and by friction may be made to 

 undergo erection. 



The mamma consists of a number of lobes separated 

 by fibrous tissue and some adipose tissue. The lobes 

 are divided and subdivided into smaller lobules, 

 which are in turn made up of alveoli. Each lobe has 

 an excretory (galactophorous) duct, and these, about 

 sixteen in number, converge to the areola, there 

 dilating into ampullae or sinuses. They then become 

 smaller again, and surrounded by areolar tissue and 

 vessels, pass through the nipple to empty on the 

 surface by separate orifices. 



Milk. Milk as obtained from the breast during 

 active secretion or lactation is an opaque, bluish- 



