THE GASTRIC JUICE. [OH. xxxi. 



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 gener- 

 ally, 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 thia 

 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 

 secretion, being at first somewhat enlarged and after secretion they 

 are somewhat shrunken. They are also called oxyntic (acid- form- 

 ing) cells, because they secrete the hydrochloric acid of the juice. 

 Heidenhain succeeded in making in one dog a cnl-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 formation 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 considers that it 

 originates by the interaction of the calcium chloride with the 

 di-sodium hydrogen phosphate of the blood, thus : 



2Na 2 HP0 4 + 3CaCl 2 = Ca 3 (P0 4 ) 2 + 4NaCl + 2HC1 



[di-sodium [calcium [calcium [sodium [hydro- 



hydrogen chloride] phosphate] chloride] chloric 



phosphate] acid] 



or more simply by the interaction of sodium chloride and sodium 

 di-hydrogen phosphate, as is shown in the following equation : 



NaH 2 P0 4 + NaCl = Na 2 HP0 4 + HC1 



[sodium di- [sodium [di-sodium [hydro- 

 hydrogen chloride] hydrogen chloric 

 phosphate] phosphate] acid] 



The sodium di-hydrogen phosphate in the above equation is 



