138 DIGESTION. 



food. We have even seen tough and indigestible pieces of tendon, 

 introduced through the fistula, expelled again in a few minutes, one 

 after the other, without exciting the flow of a single drop of acid 

 fluid ; while pieces of fresh meat, introduced in the same way, pro- 

 duced at once an abundant supply. In other instances, on the con- 

 trary, the introduction of metallic catheters, &c., into the empty 

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

 menting upon dogs that have been kept without food during various 

 periods of time and then killed by section of the medulla oblongata, 

 we have usually, though not always, found the gastric mucous mem- 

 brane to present a distinctly acid reaction, even after an abstinence 

 of six, seven, or eight days. There is at no time, however, under 

 these circumstances, any considerable amount of fluid present in 

 the stomach ; but only just sufficient to moisten the gastric mucous 

 membrane, and give it an acid reaction. 



The gastric juice, which is obtained by irritating the stomach 

 with a metallic catheter, is clear, perfectly colorless, and acid in 

 reaction. A sufficient quantity of it cannot be obtained by this 

 method for any extended experiments ; and for that purpose, the 

 animal should be fed, after a fast of twenty-four hours, with fresh 

 lean meat, a little hardened by short boiling, in order to coagulate 

 the fluids of the muscular tissue, and prevent their mixing with the 

 gastric secretion. No effect is usually apparent within the first five 

 minutes after the introduction of the food. At the end of that time 

 the gastric juice begins to flow ; at first slowly, and in drops. It is 

 then perfectly colorless, but very soon acquires a slight amber 

 tinge. It then begins to flow more freely, usually in drops, but 

 often running for a few seconds in a continuous stream. In this 

 way from sij to siiss may be collected in the course of fifteen 

 minutes. Afterward it becomes somewhat turbid with the debris 

 of the food, which has begun to be disintegrated ; but from this it 

 may be readily separated by filtration. After three hours, it con- 

 tinues to run freely, but has become very much thickened, and 

 even grumous in consistency, from the abundant admixture of 

 alimentary debris. In six hours after the commencement of diges- 

 tion it runs less freely, and in eight hours has become very scanty, 

 though it continues to preserve the same physical appearances as 

 before. 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 collected, and separated by 



