384 FOOD AND DIGESTION 



exact neutralization with i per cent, sulphuric acid. Test for protein reac- 

 tions. Peptone gives a rose color in the biuret reaction. The xanthoproteic 

 reaction gives the color change, but not the usual precipitate. Peptone is re- 

 dissolved from its alcoholic precipitate without change. It is dialyzable. 



15. Action of Rennin. Add a solution of commercial rennin (jun- 

 ket powder), or of the extract of gastric mucous membrane of the fourth 

 stomach of the calf, to 5 c.c. of milk and let stand for a few minutes. Repeat 

 the test with artificial gastric juice. Also with neutral gastric juice. In each 

 case the milk will form a jelly-like clot, which is firmer in the test-tube con- 

 taining commercial rennin. In the test-tube containing artificial gastric 

 juice the milk is first coagulated, then slowly dissolved or digested. This 

 clotting is due to the special coagulating enzyme, rennin. 



III. PANCREATIC JUICE AND PANCREATIC DIGESTION. 



1 6. The Secretion of Pancreatic Juice. If a dog containing a pan- 

 creatic fistula made by Pawlow's method is available, then try the experi- 

 ment of feeding the animal and noting the rate of secretion of pancreatic 

 juice through a period of two hours. When the gastric digestion has pro- 

 ceeded to the point where the acid chyme may be supposed to have entered 

 the duodenum, then a sharp increase in the flow of pancreatic juice takes 

 place. This increased activity will last through a period of two or three 

 hours or more. It is produced either by nerve reflexes (Pawlow) or by the 

 influence of the secretin produced by the intestinal mucous membrane when 

 stimulated by acid. 



17. Influence of Secretin on the Rate of Secretion. Make an ex- 

 tract of the intestinal mucous membrane, preferably from the duodenum, 

 by scraping off the membrane, grinding it to a pulp, and extracting it over a 

 water-bath in o . 2 per cent, hydrochloric acid, and filtering. 



Anesthetize a large dog, open the abdomen, isolate the pancreatic duct, 

 introduce a cannula, and arrange for the collection of pancreatic juice. Intro- 

 duce a cannula into the saphenous vein and connect it with a buret containing 

 the extract of secretin already prepared. Inject 5-c.c. quantities of the 

 secretin solution into the vein at intervals of ten minutes. Measure the rate 

 of secretion of pancreatic juice by counting the drops per minute or, if the 

 secretion is rapid enough, by collecting it at intervals of five or ten minutes 

 and measuring it in a graduated pipet. 



This method will often yield enough pancreatic juice in the course of a 

 couple of hours to make the pancreatic experiments which follow. Bayless 

 and Starling call it secretin juice. 



1 8. Chemical Characters of Pancreatic Juice. Test the reaction, 

 protein, salt, etc., content of the sample of pancreatic juice collected in the 

 last experiment. 



