ALIMENTARY MECHANISMS 409 



Its chief digestive importance consists in the presence of the activating 

 enzyme, enterokinase. Enterokinase can be prepared by extracting the 

 mucous membrane of the small intestine by the method outlined for making a 

 pancreatic extract. 



To two test-tubes containing 2 cc. of artificial pancreatic juice, or pref- 

 erably containing secretin pancreatic juice, add 2 threads of fibrin. Keep one 

 for the control, to the other add 2 cc. of enterokinase solution. The test- 

 tube containing enterokinase will digest more rapidly and more effectively 

 than the other. 



V. ALIMENTARY MECHANISMS. 



26. Normal Peristalsis and the Vagus Control of the Frog Stomach 

 and Intestine. Pin a pithed frog supine on a frog board. Expose the 

 stomach and isolate the vagus. Attach a lever to the outer curvature of 

 the stomach by S-shaped hook and thread, so that the contractions register 

 as usual. Anchor the gastric mesentery by pin but avoid blood vessels. 



a. Make a continuous record on a slow drum of the normal peristalsis 

 of the stomach for 30 minutes. 



b. Stimulate the vagus nerve for 5 to 10 seconds with weak induction 

 shocks, as tested by your tongue. Mark the time of stimulation by a 

 signal magnet. Allow a long recovery period after each stimulation. 

 Repeat with stronger stimuli. 



c. Compare by direct inspection the general characteristics of gastric 

 peristalsis both before and following vagus stimulation. Does stimulation 

 induce a single contraction or a rhythm? 



d. Transfer the lever to the duodenum and record its normal con- 

 tractions. Then stimulate the vagus to test extrinsic motor nerve 

 control. 



e. Expose the small intestine of the frog just used and make obser- 

 vations by inspection without registration. Lightly pinch the pyloric 

 stomach or duodenum with a forceps. Note the time with watch and 

 determine the rate of peristalsis. Observe the final swinging movements 

 of the cloaca or rectum. Remove the intestine and measure its total 

 length. Calculate the rate of propagation per centimeter per second and 

 the total time for the wave to pass the length of the intestine. 



27. Gastro-intestinal Movements of the Cat. Use a two kilo cat 

 which has been fed ground meat four hours before. Give 10 cc. of a 10 per 

 cent, chloral hydrate solution per rectum, or 4 grams of urethane, twenty 

 minutes before the experiment. Very little ether is then required for 

 narcosis. Open the abdomen along the midline to expose the stomach and 

 intestine. Protect the visceral organs by covering with very thin wax paper. 



