154 FUNCTIONS OF NUTRITION. 



surface of the mucous membrane. According to our own observations, 

 the irritability of the gastric mucous membrane, and the readiness with 

 which the flow of gastric juice may be excited, varies considerably in 

 different animals of the same species. In dogs, we have found in one 

 instance that the gastric juice was always entirely absent in the inter- 

 vals of digestion ; the mucous membrane presenting either a neutral 

 or slightly alkaline reaction. In this animal, which was perfectly 

 healthy, the secretion could not be excited by any artificial means, such 

 as glass rods, metallic catheters, or the like ; but only by the stimulus 

 of ingested food. Indigestible pieces of tendon, introduced through 

 the fistula, were expelled in a few minutes, without exciting the flow 

 of a single drop of acid fluid ; while pieces of fresh meat, introduced 

 in the same way, produced at once an abundant supply. In other 

 instances the introduction of metallic catheters or glass rods into the 

 empty stomach has produced a scanty flow of gastric juice ; and in 

 dogs killed by section of the medulla oblongata, we have usually, 

 though not always, found the gastric mucous membrane with a dis- 

 tinctly acid reaction, even after an abstinence of six, seven, or eight 

 days. Under these circumstances there is never any considerable 

 amount of fluid in the stomach; but only enough to moisten the 

 mucous membrane, and give it an acid reaction. 



The gastric juice obtained by irritating the stomach with a metallic 

 catheter is not sufficient in quantity for extended experiments. For 

 that purpose, the animal should be fed, after a fast of twenty-four 

 hours, with fresh lean meat, slightly hardened by short boiHng, in 

 order to coagulate the fluids of the muscular tissue, and prevent their 

 mixing with the gastric secretion. Usually no effect is apparent 

 within five minutes after the introduction of food. At the end of 

 that time the gastric juice begins to flow slowly and in drops. It is at 

 first colorless, but soon acquires a slight amber tinge. It then runs 

 more freely, usually in drops, but often for a few seconds in a 

 continuous stream. In this way, from 60 to 75 cubic centimetres 

 may be collected in the course of fifteen minutes. Afterward it 

 becomes somewhat turbid with the debris of disintegrated food, 

 from which it may be separated by filtration. After three hours, 

 it continues to run freely, but much thickened and grumous in con- 

 sistency, from the admixture of alimentary debris. In six hours it is 

 less abundant, and in eight hours has become very scanty. It ceases 

 to flow altogether in from nine to twelve hours, according to the 

 quantity of food taken. For purposes of examination, the fluid 

 drawn during the first fifteen minutes after feeding should be col- 

 lected, and at once separated by filtration from accidental impurities. 



Physical Properties and Composition of the Gastric Juice. 

 Gastric juice obtained by this method is a clear, colorless, or faintly 

 amber-colored fluid, of watery consistency and acid reaction. Its 

 specific gravity does not vary much from 1010. It becomes slightly 

 opalescent on boiling. 



