270 



THE TISSUES AND MECHANISMS OF DIGESTION. 



prolonged activity, as in Fig. 83, C, the cells are still smaller, with their 

 outlines still more distinct, and the granules have disappeared almost 

 entirely, a few only being left at the extreme inner margin of each cell, 

 abutting upon the conspicuous, almost gaping lumen of the alveolus. And 



FIG. 83. 



Changes in the Parotid during Secretion. (Langley.) The figure, which is somewhat dia- 

 grammatic, represents the microscopic changes which may be observed in the living gland. A. 

 During rest. The obscure outlines of the cells are introduced to show the relative size of the 

 cells; they could not be readily seen in the specimen itself. B. After moderate stimulation. C. 

 After prolonged stimulation. The nuclei are diagrammatic, and introduced to show their ap- 

 pearance and position. 



upon special examination it is found that the nuclei are large and round. 

 In fact, we might almost take the parotid, as thus studied, to be more truly 

 typical of secretory changes than even the pancreas. For the demarcation 

 of an inner and outer zone is not a necessary feature of a secreting cell at 

 rest. What is essential is that the cell-substance manufactures material, 

 which for a while, that is during rest, is deposited in the cell, generally in 

 the form of granules but not necessarily so, and that during activity this 

 material is used up, the disappearance of the granules, when these are 

 visible, being naturally earliest and most marked at the outer portions of 

 each cell, and progressing inward toward the lumen, the whole cell becoming 

 smaller and, as it were, shrunken. 



In the cells of the parotid gland and other albuminous cells the granules 

 seen in the living or fresh cell differ from the granules seen in the pancreatic 

 cell, inasmuch as they are easily dissolved or broken up by the action of 

 alcohol, chromic acid, and the other usual hardening reagents, and hence in 

 hardened specimens have disappeared. In consequence, in sections of har- 

 dened and prepared albuminous glands the difference between resting or 

 loaded and active or discharged cells may appear not very conspicuous ; 

 and this is especially the case in the parotid gland of the rabbit when the 



FIG. 84. 



After stimulation 



Sections of the Parotid of the Rabbit. (After Heidenhain.) A. At rest, 

 of the cervical sympathetic. Both sections are from hardened gland. 



activity has been called into play by stimulation of the auriculo-temporal 

 nerve. When, however, either in the rabbit or the dog the cervical sym- 

 pathetic is stimulated, though the stimulation gives rise in the rabbit to 



