188 MUCOUS MEMBRANES 



hain (crescents of Gianuzzi). In the tubules of some glands these 

 demilunes are extremely minute, in others they occupy a consider- 

 able portion of the epithelial coat and encroach upon the glandu- 

 lar lumen. Their significance is not definitely understood. They 

 have been considered as representing either secreting cells which 

 are in a state of rest following the discharge of their secretion, 

 or as primordial cells which by reproduction give origin to true 

 mucous secreting cells. It is quite possible that both of these func- 

 tions are assumed by the several cells which compose the demilunes. 



Mucus, the product of the mucous 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 basophile 

 properties of the precipitated flocculi are so characteristic that 

 when typical mucus containing cells are once carefully observed 

 they can be thereafter most 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 

 characteristics. These cells are unquestionably capable of alter- 

 nate 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 de- 

 void of secretion and frequently presents a faintly rodded or stri- 

 ated 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 character; 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 mem- 

 brane and is surrounded 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. 



