33G ACTION ON VARIOUS TISSUES. 



are dissolved and peptonised by the gastric juice (Uffelmann). (2.) The structure- 

 less membranes (membranae proprice) 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.) The striped-muscular substance, 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, 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 haemoglobin decomposed into hosmatin and 

 a globulin-like substance; the latter is peptonised, while the former remains un- 

 changed, and is partly absorbed and transformed into bile-pigment. Fibrin is 

 easily dissolved to form propeptone and fibrin-peptone. (7.) Mucin, which is also 

 secreted by the goblet cells of the stomach, passes through the intestines un- 

 changed. (8.) Vegetable fats are not affected by the gastric juice; these cells 

 yield their protoplasmic contents to form peptones, while the cellulose of the cell- 

 wall, in the case of man at least, remains undigested. During putrefaction in the 

 intestine, some cellulose seems to be transformed into sugar. 



Why the Stomach does not digest itself. That the stomach can digest 

 living things is shown by the following facts: The limb of a living frog was intro- 

 duced through a gastric fistula into the stomach of a dog (Cl. Bernard) the ear of a 

 rabbit (Pavy) was also introduced and both were partly digested. The margins of 

 a gastric ulcer and of gastric fistulae in man are attacked by the gastric juice. John 

 Hunter (1772) discussed the question as to why the stomach does not digest itself. 

 Not unfrequently after death the posterior wall of the stomach is found digested, 

 [more especially if the person die after a full meal and the body be kept in a warm 

 place, whereby the contents of the stomach may escape into the peritoneum. 

 Cl. Bernard showed, that if a rabbit be killed and placed in an oven at the 

 temperature of the body, the walls of the stomach are attacked by its own 

 gastric juice. Fishes also are frequently found with their stomach partially 

 digested after death]. It would seem, therefore, that so long as the circulation 

 continues, the tissues are protected from the action of the acid by the alkaline 

 blood; this action cannot take place if the reaction be alkaline (Pavy). Ligature 

 of the arteries to the stomach, according to Pavy, causes digestive softening of the 

 gastric mucous membrane. The thick layer of mucus may also aid in protecting 

 the stomach from the action of its own gastric juice (Cl. Bernard). 



167. Gases in the Stomach. 



The stomach always contains a certain quantity of gases, which are 

 derived partly from the gases swallowed with the saliva, partly 

 from gases which pass backwards from the duodenum, and partly from 

 air swallowed directly. 



If the larynx and hyoid bone (p. 311) are suddenly and forcibly raised upwards 

 and forwards, there passes into the space behind the larynx a considerable amount 

 of air, which, on the latter regaining its position, is swallowed, owing to the 

 peristalsis of the oesophagus. We can feel the passage of such a mass of air as it 

 passes along the oesophagus. In this way a considerable volume of air may be 

 swallowed. 



