482 THE GASTRIC JUICE [CH. XXXL 



pyloric glands, in the pyloric part of the stomach, have long ducts 

 and short tubules lined with cubical granular cells. There are no 

 parietal cells. 



The central cells of the cardiac glands and the cells of the pyloric 

 glands are loaded with granules. During secretion they discharge 

 their granules, those that remain being chiefly situated near the lumen, 

 leaving in each cell a clear outer zone. These are the cells that 

 secrete the pepsin. Like secreting cells generally, they select certain 

 materials from the lymph that bathes them; these materials are 

 worked up by the protoplasmic activity of the cells into the secretion, 

 which is then discharged into the lumen of the gland. The most 

 important substance in a digestive secretion is the ferment. In the 

 case of the gastric juice this is pepsin. We can trace an intermediate 

 step in this process by the presence of the granules. The granules 

 are not, however, composed of pepsin, but of a mother-substance 

 which is readily converted into pepsin. We shall find a similar 

 ferment precursor in the cells of the pancreas, and the term zymogen 

 is applied to these ferment precursors. The zymogen in the gastric 

 cells is called pepsinogen. The rennet-ferment or rennin that causes 

 the curdling of milk is distinct from pepsin, but is formed by the 

 same cells. 



The parietal cells undergo merely a change of size during secre- 

 tion, being at first somewhat enlarged, and after secretion they are 

 somewhat shrunken. They are also called oxyntic (acid -forming) cells, 

 because they secrete the hydrochloric acid of the juice. Heidenhain 

 succeeded in making in one dog a cul-de-sac of the fundus, in another 

 of the pyloric region of the stomach; the former secreted a juice 

 containing both acid and pepsin ; the latter, parietal cells being 

 absent, secreted a viscid alkaline juice containing pepsin. The forma- 

 tion of a free acid from the alkaline blood and lymph is an important 

 problem. There is no doubt that it is formed from the chlorides of 

 the blood and lymph, and of the many theories advanced as to how 

 this is done, Maly's is, on the whole, the most satisfactory. He con- 

 siders that it originates by the interaction of the calcium chloride 

 with the di-sodium hydrogen phosphate of the blood, thus : 



2Na 2 HPO 4 + 3CaCl 2 = Ca 3 (PO 4 ) 2 + 4NaCl + 2HC1, 



[Di-sodium hydrogen [Calcium [Calcium [Sodium [Hydrochloric 



phosphate.] chloride.] phosphate.] chloride.] acid.] 



or more simply by the interaction of sodium chloride and sodium di- 

 hydrogen phosphate, as is shown in the following equation : 



NaH 2 PO 4 + NaCl = Na 2 HPO 4 + HC1. 



[Sodium di-hydrogen [Sodium [Di-sodium hydrogen [Hydro- 

 phosphate.] chloride.] phosphate.] chloric acid.] 



The sodium di-hydrogen phosphate in the above equation is 



