ACTION OF GASTRIC JUICE ON THE VARIOUS TISSUES. 25 1 



juice quite distinct from pepsin the milk-curdling ferment which, quite inde- 

 pendently of the acid, precipitates the casein either in neutral or alkaline solutions. 

 It is this ferment or rennet which is used to coagulate casein in the making of 

 cheese. [Rennet is an infusion of the fourth stomach of the calf in brine ( 231). 

 The ferment which coagulates milk is quite distinct from pepsin. If magnesic car- 

 bonate be added to an infusion of calf's stomach, a precipitate is obtained. The 

 clear fluid has strongly coagulating properties, while the precipitate is strongly 

 peptic] 



The action of the milk-curdling ferment is perhaps, like the action of all ferments, a hydration 

 of casein ; it is greater in the presence of 0'2 HC1. 



One part of the rennet-ferment can precipitate 800,000 parts of casein. When casein 

 coagulates, two new proteids seem to be formed the coagulated proteid which constitutes 

 cheese, and. a body resembling peptone dissolved in the whey. The addition of calcium chloride 

 accelerates, while water retards the coagulation ( 231) {Hammarsten). [A ferment similar to 

 rennet is contained in the seeds of Withania coagulans (S. Lea).] 



Casein is first precipitated in the stomach, then a body like syntonin is formed, and finally 

 peptone. During the process, a substance containing phosphorus and resembling nuclein 

 appears (Lubavin). 



There is a " lactic acid ferment" also present, which changes milk-sugar into 

 lactic acid {Hammarsten). Part of the milk-sugar is changed in the stomach and 

 intestine into grape-sugar. 



Action on Carbohydrates. Gastric juice does not act as a solvent of starch, 

 inulin, or gums. Cane-sugar is slowly changed into grape-sugar. According to 

 Uffelmann, the gastric mucus, and according to Leube, the gastric acid, are the 

 chief agents in this process. On albumenoids. During the digestion of true 

 cartilage, there is formed a chondrin-peptone, and a body which gives the sugar- 

 reaction with Trommer's test. Perfectly pure elastin yields an elastin-peptone, 

 similar to albumin-peptone, and hemi-elastin similar to hemi-albumose. A very 

 minute quantity of fat is broken up into glycerine and fatty acids. [On neutral 

 olive-oil being injected into the stomach of a dog, after several hours the pylorus 

 being plugged with an elastic bag it partly splits up and yields oleic acid (Cash 

 and Ogata).} 



[We still require further observations on the gastric digestion of fats. Richet observed in 

 his case of fistula, that fatty matters remained a long time in the stomach, and Ludwig found 

 the same result in the dog. In some dyspeptics, rancid eructations often take place towards 

 the end of gastric digestion. ] 



HI. Action on the various Tissues. (1) The gelatin yielding substance (collagen) of all the 

 connective-tissues (connective-tissue, white fibro-cartilage, and the matrix of bone), as well as 

 glutin, is dissolved and peptonised by the gastric juice. [Gelatin, when acted on by gastric juice, 

 no longer solidifies in the cold, but a gelatin-peptone is formed, which is soluble and diffusible, 

 although it differs from true peptone. In the dog, connective-tissues are specially acted on in 

 the stomach, while the other parts of organs used as food are prepared for digestion in the small 

 intestine, where the cellular and nuclear elements are digested by the pancreatic juice 

 (Bikfalvi).] (2) The structureless membranes (membranse propria?) of glands, sarcolemma, 

 Schwann's sheath of nerve-fibres, capsule of the lens, the elastic laminae of the cornea, the 

 membranes of fat-cells are dissolved, but the true elastic (fenestrated) membranes and fibres are 

 not affected. (3) Striped muscle, after solution of the sarcolemma, breaks up transversely into 

 discs, and, like non-striped muscle, is dissolved, and forms a true soluble peptone, but parts of 

 the muscle always pass into the intestine. (4) The albuminous constituents of the soft cellular 

 elements of glands, stratified epithelium, endothelium, and lymph-cells, form peptones, but the 

 nuclein of the nuclei does not seem to be dissolved. (5) The horny parts of the epidermis, 

 nails, hair, as well as chitin, silk, conchiolin, and spongin of the lower animals are indigestible, 

 and so are amyloid-substance and wax. (6) The red blood-corpuscles are dissolved, the haemo- 

 globin decomposed into hsematin and a globulin-like substance ; the latter is peptonised, while 

 the former remains unchanged, and is partly absorbed and transformed into bile-pigment. 

 Fibrin is easily dissolved to form hemi- and anti-peptone. (7) Mucin, which is also secreted 

 by the goblet-cells of the stomach, passes through the intestines unchanged. (8) Vegetable fats 

 are not affected by the gastric juice ; these cells yield their protoplasmic contents to form pep- 

 tones, while the cellulose of the cell-wall, in the case of man at least, remains undigested ( 184). 



Why the Stomach does not digest itself. That the stomach can digest living things is 

 shown by the following facts : Bernard introduced the leg of a living frog through a gastric 



