346 A MANUAL OF PHYSIOLOGY 



termed parietal from their position, oxyntic (or acid-secreting) from 

 their supposed function (Figs. 138-140). Access to the lumen of the 

 glands is provided for these deeply-placed parietal cells and for the 

 cells of the crescents by fine branching channels which enter and sur- 

 round the cells. The serous salivary glands, the pyloric glands of the 

 stomach, and the Lieberkuhn's crypts, have but a single layer of 

 epithelium ; and since there is no hepatic cell which is not in contact 

 with at least one bile-capillary, the liver may be regarded as having 

 no more. The same is true of the pancreatic alveoli, except that 

 in the centre of many of the acini a few spindle-shaped cells (centro- 

 acinar cells), apparently continued from the lining of the smallest 

 ducts, may be seen. Remarkable histological changes, evidently 

 connected with changes in functional activity, have been noticed 

 in most of the digestive glands. In discussing these, it will be 

 best to omit for the present any detailed reference to the liver, since, 

 although there are histological marks of secretive activity in this 

 gland as well as in others, and of the same general character, they 

 are accompanied, and to some extent overlaid, by the microscopic 



A B 



FIG. 136. PANCREAS IN ' LOADED ' AND * DISCHARGED ' STATE. 



A, alveolus of rabbit's pancreas, 'loaded' (resting); B, 'discharged' (active), 

 observed in the living animal (Kiihne and Lea). 



evidences of other functions (p. 511). The serous salivary glands 

 and the pancreas can be taken together ; so can the glands of the 

 various regions of the stomach ; the mucous salivary glands must 

 be considered separately. 



Changes in the Pancreas and Parotid during Secretion. 



The cells of the alveoli of the pancreas or parotid during rest, as 

 can be seen by examining thin lobules of the former between the 

 folds of the mesentery in the living rabbit, or fresh teased pre- 

 parations of the latter, are rilled with fine granules to such an 

 extent as to obscure the nucleus. In the parotid the whole cell 

 is granular, in the pancreas there is still a narrow clear zone at 

 the outer edge of the cell which contains few granules or none ; 

 in both, the divisions between the cells are very indistinct, and 

 the lumen of the alveolus cannot be made out. During activity 

 the granules seem to be carried from the outer portion of the cell 

 towards the lumen, and there discharged ; the clear outer zone 



