i86 



HISTOLOGY. 



tive granules. In fixed preparations they may appear dark and granular 

 (empty of secretion) or enlarged and somewhat clearer (full of secretion), 

 as shown in Fig. 34, p. 32. The round nucleus is generally in the basal 

 half of the cell, not far from its center (Fig. 208). Mucous cells when 

 fresh are much less refractive than serous cells. In fixed preparations they 

 are typically clear since the large area occupied by mucous secretion stains 



Man. 



Rabbit. 



Man. 



-tl 





; / Axial lumen. 



Mucous glands. Serous glands. 



FIG. 208. SECTIONS OP TUBULES, PROM LINGUAL GLANDS, ILLUSTRATING THE DIFFERENCES 



BETWEEN MUCOUS AND SEROUS GLAND CELLS. 

 b, Empty mucous cells; c, mucous cells full of secretion; d, lumen of the tubule. X 240. 



faintly. Fully elaborated mucus, however, may be colored intensely with 

 certain aniline dyes, mucicarmine, and Delafield's haematoxylin. In cer- 

 tain types of mucous cells the pale secretion area is large in all stages of 

 activity. When full of mucus, the nucleus is flattened against the base 

 of the cell, and when empty, the nucleus becomes more oval without essen- 

 tially changing its position (Fig. 208). This differs from the type of mu- 

 cous cell found in the gastric epithelium 

 in which the secretion area varies consider- 

 ably with the elaboration and discharge 

 of secretion (Fig. 35, p. 33). 



Glands may consist entirely of serous 

 or of mucous cells, but frequently they in- 

 clude cells of both sorts and are called 

 mixed glands. The mixed glands con- 

 tain some purely serous tubules or alveoli; 

 the rest consist of both mucous and 

 serous cells, so arranged that the latter 

 appear more or less crowded away 

 from the lumen. Often they form a 



layer outside of the mucous cells partly encircling the tubule or alveolus 

 and constituting a crescent [demilune]. They are shown in Fig. 216. The 

 serous cells of the crescent are in connection with the lumen by means of 

 secretory capillaries (p. 36) which branch over their surfaces, ending 

 blindly, after passing between the mucous cells (Fig. 209). Sometimes 



Intercellular 

 secretory 

 capillary. 



Crescent. 



FIG. 209. FROM A SECTION OP THE 

 SUBMAXILLARY GLAND OP A DOG. 

 X 320. 



