138 



MANUAL OF PHYSIOLOGY. 



During rest certain changes gradually appear in those gland- 

 cells which are next the lumen of the saccule. They appear to 

 swell towards the lumen, and at the same time become clear and 

 resist staining with carmine, their protoplasm becoming impreg- 

 nated with mucous-like material (mucigen), while the demi-hme 

 cells remain protoplasmic and stain easily, and are thereby readily 

 distinguished from the cell in the cavity of the saccule. 



Now, if the discharge of secretion be called for, either by normal 

 reflex excitation, or by direct stimulus of the chorda tympani 

 nerve, the cells discharge the contained specific material, some of 

 them most probably being destroyed by the act. If the active 



Cells of the Alveoli of a Serous or Watery Salivary Gland. (Langley.) 

 (A) After rest. (B) After a short period of activity, (c) After prolonged 

 period of activity. 



secretion be continued for some time, the cells return to their 

 former protoplasmic state, and the cells which have been worn 

 out are replaced by others from the demi-luue or marginal cells. 



In the glands which do not produce any mucus the brilliant 

 look of the cells after rest is wanting, but a corresponding change 

 occurs. The secreting protoplasm becomes extremely granular 

 during the resting period, and again clear after the discharge of 

 the secretion. (Fig. 67.) 



Thus it would appear that during the so-called period of rest, 

 when little or no fluid is poured into the duct, the gland-cells are 

 busy at their manufacturing process, diligently adding to their 

 stock in hand in order to be ready for a certain demand which 

 they could not meet by merely concurrent work. 



To sum up, then, we may conclude : 



