MOUTH CAVITY. 



173 



marked chroinatin network. During the formation of mucus 

 the granules increase in size, and finally are converted into 

 fluid material. The meshes of the protoplasmic network 

 become wider as the mucus fills them. The cell grows in size 

 and has a clear, transparent appearance. The nucleus becomes 

 irregular and is pressed into a corner of the cell or against the 

 membrana propria. In the immediate neighborhood of the 

 nucleus there is a small quantity of unchanged protoplasm. 

 During active secretion the mucus escapes from the cell, and the 

 granular protoplasm near the nucleus increases in amount. The 



FIG. 128. 



Serous cells of a v 



demilune cut 



tangentially <.( 



Cells full of. 

 secretion 



Connective tissue 

 ith blood-vessels 



mucous cell 



Empty mucous cell 



Secretory ^--^ 

 capillaries 



Demilunes of Qianuzzi 

 From a section through a human sublingual gland. (Preparation by R. Krause.) x o60. 



nucleus becomes oval and the chromatin framework more distinct, 

 and we have again the appearance of an empty cell (Fig. 128). 

 A mucous cell which has just emptied out its secretion, and 

 a serous cell are very similar in appearance. Usually cells in 

 the same tubule are found in different stages of secretion, so 

 that their appearance is very different. Sometimes a whole 

 tubule is made up of one kind of cell, but in a great many 

 glands both serous and mucous cells are present in the same 

 tubule, and we have then to deal with mixed glands. The 

 parotid in all animals is a purely serous gland ; also the sub- 

 maxillary of rabbits, and the small glands in the region of the 



