256 MUCOUS MEMBRANES GLANDS 



cells which compose the demilunes. Many of these cells contain an 

 independent,, intracellular, secretory, canalicular system, which indi- 

 cates a specific and independent functional role. 



Mucus, the product of the mucus-secreting cells, possesses peculiar 

 properties. In the fresh condition it has a clear, glairy appearance and 

 a pearly white color. Acted upon by alcohol or acids it gives a heavy 

 precipitate of stringy white flocculi. Within the tissues these delicate 

 flocculi stain slightly, with basic dyes and readily with the muchematin 

 and mucicarmin of Mayer. The very clear glairy appearance of the 

 fluid and the slightly basophil properties of the precipitated flocculi are 

 so characteristic that when typical mucus-containing cells are once care- 

 fully observed they can be thereafter readily distinguished from other 

 types of epithelium. 



Serous-secreting cells differ greatly in appearance with the vary- 

 ing character of their secretions, yet they present certain general char- 

 acteristics. These cells are unquestionably capable of alternate phases 

 of secretory activity and comparative rest. At the end of a period of 

 activity they appear shrunken and small, and the lumen of their tubule 

 is consequently increased in size. Their nucleus is centrally located, 

 and their cytoplasm is relatively devoid of secretion and frequently 

 presents a faintly rodded or striated appearance. 



During rest secretion accumulates within the cell, and the cytoplasm 

 consequently becomes either clearer or more granular, according as the 

 nature of the secretion is watery, or is granular and zymotic in char- 

 acter; thus the secreting cells of the sweat glands become clearer as 

 their secretion accumulates, whereas those of the pancreas become more 

 granular. 



As a rule the pre-secretion accumulates at the central end of the cell, 

 the nucleus is thus crowded toward the basement membrane and is sur- 

 rounded by the least altered cytoplasm. The whole cell becomes swollen 

 and distended by the accumulated secretion and the tubular lumen is 

 consequently diminished in size or even occluded. 



Finally the period of secretory activity arrives, and the secretion 

 is poured into the glandular lumen; the cells become shrunken and the 

 lumen of the tubule correspondingly dilated. The cytoplasm returns 

 to its former condition; if the secretion is of a granular character the 

 cell becomes clearer, but if watery the cytoplasm acquires a finely granu- 

 lar appearance. The nucleus resumes its former central location and 

 the cell enters upon a second period of constructive and accumulative 

 activity. 



