

ACTION OF THE GASTRIC SECRETIONS. 547 



Action of the G-astric Juice, and Mucus of the Stomach. 



It is the gastric juice, secreted by the peptic glands, which accom- 

 plishes the act of gastric digestion ; the secretion of the racemose 

 glands, lined with columnar epithelium, found near the pyloric end of 

 the stomach, is supposed not to participate in this office, but it may 

 act in the further conversion of starch into sugar. In this stage of 

 digestion, albuminoid and gelatinoid substances are specially acted 

 upon, and are reduced to a pulpy mixture, containing the so-called 

 albuminose or peptone. The solid or insoluble forms, such as coagu- 

 lated albumen, santonin, and fibrin, are slowly dissolved: certain of 

 the soluble forms, as the casein in milk, and the albumen in vegetable 

 juices, are first precipitated, and then dissolved ; whereas fluid albu- 

 men, as the raw white of egg, remains in solution whilst it is being 

 converted into albuminose. Albuminose resembles the albuminoid 

 bodies in chemical composition, though differences will probably here- 

 after be detected in it. Whatever the peculiarity of the albuminoid 

 body, whether it be albumen, syntonin, fibrin, or casein, gluten, or 

 legumin, it is transformed into an almost identical albuminose. More- 

 over, this albuminose, or peptone, possesses properties which distin- 

 guish it from the albuminoids. Thus, it is no longer coagulable by 

 heat, nor by the action of nitric acid, though still precipitable by 

 tannic acid, metallic salts, and strong alcohol; it is soluble in all pro- 

 portions in water, so much so, that the act of digestion of the albu- 

 minoids, or their conversion into albuminose, has been referred hypo- 

 thetically to a kind of hydration of the albuminoids, or a taking up 

 by them of certain atoms of water, just as the hydration of starch or 

 dextrin appears to be a step in their conversion into sugar. Gelatin, 

 and the gelatin-yielding tissues, furnish a special kind of peptone, a 

 viscid fluid, which does not, according to some, gelatinize or stiffen in 

 the cold. The transformation of albuminoid and gelatinoid substances 

 into the ultimate albumen and gelatin peptones, is not sudden, but is 

 characterized by intermediate stages, in which less soluble forms of 

 these substances appear, named parapeptones. Parapeptone is pre- 

 cipitated, in the form of flocculi, from the peptones, when their mixed 

 acid solution is neutralized by an alkali ; it is insoluble in water, 

 though gradually dissolved by weak acid and alkaline solutions. The 

 peptone, as already said, is highly soluble in water, and precipitable 

 by tannic acid, alcohol, and metallic salts. When a solution of pep- 

 tone is injected into the blood of an animal, it does not appear in the 

 renal excretion; but when albumen, dissolved in very weak hydro- 

 chloric acid, is em'ployed in a similar manner, albumen is found in the 

 urine. These facts indicate that a true metamorphosis is effected in 

 the albuminoid constituents of food. The peptone ultimately pro- 

 duced, is not only freely soluble in water, but most readily permeates 

 moist animal membranes, and hence is a substance admirably fitted 

 for absorption. 



The gastric juice has no peptic action upon either the amylaceous 

 or oleaginous constituents of food. 



