CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 411 



rise to mucin, and which we might call mucigen. And we might 

 further infer that during the act of secretion the granules of 

 mucigen are transformed into masses of mucin and so discharged 

 from the cell. Under this view the appearances presented by the 

 hardened glands, as distinguished from the living glands, might be 

 interpreted as indicating that under the influence of the reagents 

 employed, the mucigen of the loaded cells had undergone the 

 transformation into mucin without being discharged from the cells. 

 Up to the present however it has not been found possible to isolate 

 from the gland any definite body, capable of being converted 

 into mucin, and there are some reasons for thinking that not 

 only the granules but part also of the substance between 

 them contributes to the formation of mucin. Apart from this 

 complication, however, the general course of events in the mucous 

 cell seems to be the same as in the pancreatic cell ; the cell- 

 substance manufactures and loads itself with a special product, 

 (or special products) ; during the act of secretion, this product, 

 undergoing at the time a certain amount of change, is discharged 

 from the cell to form part of the secretion, and the cell-substance, 

 stirred up to increased growth, subsequently manufactures a new 

 supply of the product. 



236. The 'central' or 'chief cells of the gastric glands 

 also exhibit similar changes. In such -an animal as the newt 

 these cells may, though with difficulty, be examined in the living 

 state. They are then found to be studded with granules when 

 the stomach is at rest. During digestion these granules become 

 much less numerous and are chiefly gathered near the lumen, 

 leaving in each cell a clear outer zone. And in many mammals 

 the same abundance of granules in the loaded cell, the same 

 paucity of granules for the most part restricted to an inner zone 

 in the discharged cell, may be demonstrated by the use of osmic 

 acid, Fig. 68. 



When the stomach is hardened by alcohol these changes, like 

 the similar changes in an albuminous cell, are obscured by the 

 shrinking of the ' granules ' or by their swelling up and becoming 

 diffused through the rest of the cell-substance ; so that though, in 

 sections so prepared, very striking differences are seen between 

 loaded and discharged cells, these are unlike those seen in living 

 glands. In specimens taken from an animal which has not 

 been fed for some time, the central cells of the gastric glands 

 are pale, finely granular, and do not stain readily with carmine 

 and other dyes. During the early stages of gastric digestion, 

 the same cells are found somewhat swollen, but turbid and 

 more coarsely granular ; they stain much more readily. At 

 a later stage they become smaller and shrunken, but are even 

 more turbid and granular than before, and stain still more 

 deeply. This, is true, not only of the central cells in the cardiac 

 glands, but also of the cells of which the pyloric glands are built 



