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there discharged. The clear outer zone of the pancreatic cell grows 

 broader and broader at the expense of the inner granular zone, until 

 at last the granular zone may in its turn be reduced to a narrow 

 contour line around the lumen (Fig. 153). In the uniformly clouded 

 parotid cell a similar change takes place; a transparent outer zone 



arises; and, after prolonged 

 secretion, only a thin edging 

 of granules may remain at 

 the inner portion of the cell 

 (Fig. 154). In both glands 

 the outlines of the cells be- 

 come more clearly indicated, 

 and a distinct lumen can 

 now be recognized. The 

 cells are smaller than they 

 A B are during rest. 



A , alveolus of rabbit's pancreas, 

 (resting) ; B, ' discharged ' 



Fig. 153-- 

 ' loaded 



(active), observed in the living animal 

 (Kiihne and Lea). 



The disappearance of 

 granules from without in- 

 wards during activity sug- 

 gests that these are manu- 

 factured products eliminated in the secretion, and they are generally 

 spoken of as zymogen granules. 



Bensley, who has made a careful study of the pancreas in the 

 guinea-pig, has been able to distinguish, even in fresh preparations 

 examined in the animal's own serum, but better after staining with 

 such a dye as neutral red, another kind of granules, which he regards 



Fig. 154. Alveoli of Parotid Gland: A, at Rest; B, after a Short Period of Activity; 

 C, after a Prolonged Period of Activity (Fresh Preparations) (Langley). In A 

 and B the nuclei are obscured by the granules of zymogen. 



as zymogen granules in the course of formation, and therefore 

 designates prozymogen granules. The resting acini show a clear 

 basal zone which is unstained, and a zone next the lumen containing 

 coarse zymogen granules which are faintly stained. In the active 

 gland e.g.. after a meal or after the injection of secretin (p. 407) 

 prozymogen granules which stain much more intensely than the 

 zymogen granules with neutral red make their appearance between 

 the zymogen granules, now much reduced in number and size, and 



