DIGESTION 



323 



moved towards the lumen in activity, discharged as mucin 

 in the secretion. It has been asserted that not only is the 

 protoplasm lessened in the loaded cell and renewed after 

 activity, but that many of the mucigenous cells may be 

 altogether broken down and discharged, their place being 

 supplied by proliferation of the small cells of the demilunes. 

 This conclusion, however, is not supported by sufficient 

 evidence. But the fact on which we would specially insist 

 is that the granules of the resting mucigenous cell may be 

 looked upon as a mother-substance from which the mucin 

 of the secretion is derived ; they are not actual, but potential, 

 mucin. 



So in the pancreas, the serous or albuminous salivary 



FIG. 105. Mucous CELLS (FROM SUBMAXILLARY OF DOG) IN REST 

 AND ACTIVITY (LANGLEY). 



A, B, fresh ; A', B', after treatment with dilute acetic acid ; A", B", alveoli 

 hardened in alcohol and stained with carmine. A, A' and A" represent the loaded ; 

 B, B' and B", the discharged condition. 



glands, and the glands of the stomach, there is every reason 

 to believe that the granules which appear in the intervals of 

 rest, and are moved towards the lumen and discharged 

 during activity, are the precursors, the mother-substances, of 

 important constituents of the secretion. These granules are 

 sharply marked off from the protoplasm in which they lie 

 and by which they are built up. By every mark, by their 

 reaction to stains, for instance, they are non-living sub- 

 stance, formed in the bosom of the living cell from the raw 

 material which it culls from the blood, or, what is more 

 likely, formed from its own protoplasm, then shed out in 

 granular form and secluded from further change. The 



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