482 THE HUMAN BODY 



the lining cells near the deeper end are commonly different in 

 character from the rest; and around that part of the gland the 

 blood-vessels form a closer network. These deeper cells form the 

 true secreting elements of the gland, and the passage, lined with 

 different cells, leading from them to the surface, and serving merely 

 to carry off the secretion, is known as the gland-duct. When the 

 duct is undivided the gland is simple; but when, as is more usual, 

 it is branched and each branch has a true secreting part at its 

 end, we get a compound gland, tubular (G) or racemose (F, H) 

 as the case may be. In such cases the main duct, into which 

 the rest open, is often of considerable length, so that the se- 

 cretion is poured out at some distance from the main mass of the 

 gland. 



A fully formed gland, H, thus comes to be a complex structure, 

 consisting primarily of a duct, c, ductules, dd, and secreting re- 

 cesses, ee. The ducts and ductules are lined with epithelium which 

 is merely protective and differs in character from the secreting 

 epithelium which lines the deepest parts. Surrounding each sub- 

 division and binding it to its neighbors is the gland stroma formed 

 of connective tissue, a layer of which also commonly envelops the 

 whole gland, as its capsule. Usually on looking at the surface of a 

 large gland it is seen to be separated by partitions of its stroma, 

 coarser than the rest, into lobes, each of which answers to a main 

 division of the primary duct; and the lobes are often similarly di- 

 vided into smaller parts or lobules. In the connective tissue be- 

 tween the lobes and lobules blood-vessels penetrate, to end in fine 

 capillary vessels around the terminal recesses. They never pene- 

 trate the basement membrane. Lymphatics and nerves take a 

 similar course; there is reason to believe that the nerve-fibers 

 penetrate the basement membrane and become directly united 

 with the secreting cells of some glands. 



The Secretory Process. The function of glands is to elaborate 

 and pour out a liquid, the secretion. It is obvious that the ulti- 

 mate source of the secretion is the blood circulating through the 

 gland. The digestive secretions, as we have already seen, contain, 

 in addition to water, and inorganic salts, special chemical sub- 

 stances, the enzyms, which are different in different glands. It 

 is easy to believe that the water and salts of the gland, since they 

 are precisely the same as occur in blood, may be withdrawn from 



