148 MANUAL OF PHYSIOLOGY. 



occurs here, and since the stimulus comes into close contiguity 

 with the secreting cells, it seems quite as probable that these ele- 

 ments are excited to activity by direct stimulation of their pro- 

 toplasm. 



As in the salivary glands, so in the gastric tubes, the cells show 

 some structural changes which accompany with great regularity 

 their periods of rest and activity, and therefore may be concluded 

 to be the indications of the internal processes belonging to the 

 production of the specific materials of their secretion. 



It appears probable that the chief secretory activity resides in 

 the small central cells, and not in the large ovoid border-cells, 

 since no distinct changes can be seen in the latter, and the smaller 

 gland cells seem to contain the pepsin, for if the mucous mem- 

 brane be treated with weak hydrochloric acid, these central gland- 

 cells are rapidly dissolved by a process of digestion, while the 

 border-cells simply swell up and become more transparent. So 

 that the outer ovoid cells have no title to their former name of 

 " peptic cells/' 



The central cells of the gastric glands are finely granular, pale, 

 protoplasmic masses, and continue so during the time when the 

 stomach is empty and the glands not secreting. In the earlier 

 stages of digestion these cells swell up and become turbid and 

 coarsely granular, and stain more readily with the aniline dyes. 

 As the digestive process goes on the cells again diminish in size, 

 but are found to contain a large quantity of peculiar granules, 

 which are discharged from the cell before its return to the ordi- 

 nary state of rest. The cells are said to be rich in pepsin in pro- 

 portion to their size; when swollen during active digestion they 

 contain much pepsin, when small, during hunger, they contain 

 but little. 



It would therefore appear that the pepsin of the gastric juice 

 is produced as a distinct and new manufacture by the central 

 cells of the peptic glands, and not by the other cells. Structural 

 changes have also been followed out in the so-called mucous 

 glands and in glands without any of the ovoid border cells which, 

 taken with the fact that the alkaline secretion of the pyloric end 

 of the stomach, where the mucous glands abound, is capable of 



