MUCOUS GLANDS. 



71 



are larger and lie in the connective tissue separating the 

 lobules. By the union of the interlobular ducts the large 

 common duet or ducts of the whole gland are formed. 



According to the nature of their secretion and corresponding 

 characteristics of the gland-cells, most secretory glands are 

 divisible into serous glands, mucous 

 FIG. 35. glands, and fatty glands. 



Serous glands (Fig. 35), as the parotid 

 and pancreas, secrete limpid watery fluids 

 or solutions. The secreting-cells are 

 spheroidal or polyhedral, granular, dark 

 and opaque, stain deeply, and have rounded 

 nuclei nearly centrally located. The ap- 



Alveolusof serous gland J 



(Schieflerdecker). pearance ot the cells varies somewhat 

 according to the stage of secretion. When, 

 after resting for a time, they are charged with secretion, they 

 are distended, clearer, less opaque, stain less deeply, and contain 

 an abundance of granules. After being exhausted by pro- 

 longed secretion they are shrunken or diminished in size ; 

 darker, more opaque, and more deeply 

 stained (from condensation of the pro- 

 toplasm) ; and less granular, having 

 discharged their granular contents into 

 the lumen of the gland. 



Mucous glands (Fig. 36), as the sub- 

 lingual, secrete a viscid, mucinous 

 fluid, w r hich lubricates the mucous sur- 

 faces. Goblet epithelium-cells secrete 

 a similar substance, and the character- Alveolus 

 istics of these cells are very similar 

 to those of the cells of mucous glands. Small racemose 

 mucous glands are widely distributed in mucous membranes, 

 having their alveoli in the submucosa and their ducts opening 

 on the surface. The secreting-cells of mucous glands, when 

 in the resting stage and distended with their mucinous secre- 

 tion, are large and swollen, unstained, clear, and transparent, 

 especially in the superficial portion ; their nuclei and body- 

 protoplasm are crowded well toward the bases of the cells. 

 When exhausted by continued activity they are smaller, less 

 clear, and more granular in appearance. 



FIG. 36. 



m KP US gland ' 



