244 



SECRETION OF GASTRIC JUICE. 



[Composition of Gastric Juice (Hoppc-Seylcr after C. Schmidt). 



Good human saliva is not so dilute or so poor in HC1 as I. Szabo has found even 3 of HC1 

 per 1000 in man.] 



164. SECRETION OF GASTRIC JUICE. After the discovery of the two 

 kinds of glands in the stomach and the two kinds of cells in the fundus-glands, 

 the question arose as to whether the different constituents of gastric juice were 

 formed by different histological elements. 



Changes of the Cells during Digestion. During the course of digestion, the cells of the 

 fundus (and pyloric glands, dog) undergo important changes {Heidenhain). During hunger, the 

 chief cells are clear and large, the parietal investing-cells are small, the pyloric cells clear and 

 of moderate size. During the first six hours of digestion, the chief cells become enlarged and 

 moderately turbid or granular, the parietal cells also enlarge, while the pyloric cells remain 

 unchanged. The chief cells become diminished and more turbid or granular until the ninth 

 hour, the parietal cells are still swollen, and the pyloric cells enlarge. During the last hours 

 of digestion, the chief cells again become larger and clearer, the parietal cells diminish, the 

 pyloric cells decrease in size and become turbid (figs. 183 and 184). 



[Langley gives a different description of the appearances presented by these cells. The 

 results may be reconciled by remembering that the gland-cells were examined under different 

 conditions. The secretory cells consist of a cell-substance composed of (a) a framework of living 

 protoplasm, either in the form of an intracellular fibrillar network, or in flattened bands. The 

 meshes of this framework enclose at least two chemical substances, viz., (b) a hyaline substance 

 in contact with the framework, and (c) spherical granules which are embedded in the hyaline 

 substance. During active secretion, the granules decrease in number and size, the hyaline sub- 

 stance increases in amount, the network grows. This is the reverse of what is stated above as the 

 observation of Heidenhain, but the granular appearance described by Heidenhain after secretion 

 is very probably due to the action of the hardening agent, alcohol. Langley found that in the 

 living condition, or after the use of osmic acid, in some animals at least, the chief cells are 

 granular during rest, but during a state of activity two zones are differentiated, an outer one, 

 which is clear, owing to the disappearance of the granules, and an inner more or less granular 

 one. Granules reappear in the outer part after rest. During digestion, the parietal cells 

 increase in size, but do not become granular. In all cells containing much pepsinogen, distinct 

 granules are present, and the quantity of pepsinogen varies directly with the number and size 

 of the granules. In the glands of some animals there is little difference between the resting 

 and active phases. Compare Serous Glands, 143, and Pancreas, 168.] 



The pepsin is formed in the chief cells (Heidenhain). When these are clear and 

 large, they contain much pepsin ; when they are contracted and turbid, the amount is 

 smalL The pyloric glands are also said to secrete pepsin, but only to a small extent. 

 Pepsin accumulates during the first stage of hunger, and it is eliminated during 

 digestion and also during prolonged hunger. Pepsin as such, is not present within 

 the cells, but only as a " mother-substance, " a pepsinogen-sub stance (zymogen), or 

 propepsin, which occurs in the granules of the chief cells. This zymogen, or mother- 

 substance, by itself, has no effect upon proteids ; but if it be treated with hydrochloric 

 acid or sodium chloride, it is changed into pepsin. Pepsin and pepsinogen may be 

 extracted from the gastric mucous membrane by means of water free from acids. 



[Pepsinogen and Pepsin. Glycerine extracts very little pepsin from the perfectly fresh 

 gastric mucous membrane, but a large amount is afterwards obtained by extracting it with 



