MUCOUS MEMBRANES AND GLANDS. 



141 



FIG. 169. 



The mucous glands secrete a clear, viscid, homogeneous sub- 

 stance, or mucine, having little affinity for carmine, but staining 

 deeply with haematoxylin. During rest the cells of such glands 

 become loaded and distended with the mucoid secretion, while the 

 nuclei are crowded to the periphery of the cells ; under these condi- 

 tions the cells lining the acini appear clear with well-defined outlines, 

 and, on the sides next the basement-mem- 

 brane, present a thin zone containing the 

 displaced nuclei and granular protoplasm. 

 After prolonged secretion the exhausted 

 cells contain relatively little mucoid sub- 

 stance ; hence the threads of the protoplasm 

 are no longer widely separated, but are 

 more closely placed ; in consequence of 

 these changes the cells assume appearances 

 resembling those of the elements of the 

 serous glands, being smaller, darker, and 

 more granular than the cells of the quies- 

 cent mucous gland. 



In the acini of mucous glands small crescentic groups of granular, 

 deeply-staining cells are often seen lying between the clearer elements 

 and the basement-membrane ; these are the crescents of Gian- 

 nuzzi, or the demi-lunes of Heidenhain, the significance of 

 which has caused extended discussion. The recent researches of 



FIG. 170. 



Lingual glands from tongue of 

 cat : a, b, the serous and the 

 mucous acini containing respec- 

 tively the granular and the clear 



cells. 



r a 



A and B, serous and mucous acini in different stages of functional activity : r, condition of rest, 

 the cells being gorged with secretion ; a, condition of exhaustion after great activity : following the 

 discharge of the secretion the elements of the protoplasm become more closely placed, producing an 

 appearance of increased granularity. 



Kuchenmeister, Solger, R. Krause, and others, have shown that 

 these crescents are composed of cells identical with those filling the 

 acini of the serous glands. The crescents, therefore, are groups of 

 serous cells, compressed and displaced by the preponderating mucous 

 elements, which add their albuminous secretion to that of the mucous 

 gland. Glands containing the crescents are to be classed as mixed, 

 or muco-serous. 



The vascular supply of glands is always rich. The larger blood- 

 vessels, conveyed by the submucosa, send off branches into the 



