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HAND-BOOK OF PHYSIOLOGY. 



the sympathetic, the cells become smaller and their contents more opaque; 

 the granules first of^all disappearing from the outer part of the cells, and 

 then being found only at the extreme inner part and contiguous border of 

 the cell. The nuclei reappear, as does also the lumen. (2) In the true 

 mucus-secreting glands, as the sublingual of man and other animals, and 



FIG. 16? 



FIG. 168. 



FIG. 167. From a section through a true salivary gland, a, the gland alveoli, lined with albu- 

 minous " salivary cells; 11 b, intralobular duct cut transversely. (Klein and Noble Smith.) 



FIG. 168. From a section through a mucous gland in a quiescent state. The alveoli are lined with 

 transparent mucous cells, and outside these are the demilunes of Heidenhain. The cells should have 

 been represented as more or less granular. (Heidenhain.) 



in the submaxillary of the dog, the tubes are larger, contain a larger 

 lumen, and also have larger cells lining them. The cells are of two kinds, 

 (a) mucous or central cells, which are transparent columnar cells with, 

 nuclei near the basement membrane. The cell substance is made up of a 



fine network, which in the resting state 

 contains a transparent substance called 

 mucigen, during which the cell does not 

 stain well with logwood (Fig. 168). 

 When the gland is secreting, mucigen 

 is converted into mucin, and the cells 

 swell up, appear more transparent, and 

 stain deeply in logwood (Fig. 109). 

 During rest, the cells become smaller 

 and more granular from having dis- 

 charged their contents, and the nuclei 

 appear more distinct, (b) Semilunes of 

 Heidenhain (Fig. 168), which are cre- 

 scentic masses of granular parietal cells found here and there between the 

 basement membrane and the central cells. These , cells are small, and 

 have a very dense reticulum, the nuclei are spherical, and increase in size 

 during secretion. In the mucous gland there are some large tubes, lined 

 with large transparent central cells, and have besides a few granular 

 parietal cells; other small tubes are lined with small granular parietal 



FIG. 169. A part of a section through a 

 mucous gland after prolonged electrical 

 stimulation. The alveoli are lined with small 

 granular cells. (Lavdovski.) 



