314 PHYSIOLOGY FOR DENTAL STUDENTS. 



the. lingual nerve, central to the origin of the chorda tympani, and 

 the lingual nerve is divided central to the ligature. Two ligatures are 

 passed under Wharton's duct and one is tied. The chorda tympani is 

 stimulated with tetanizing shocks from the induction coil. Wharton's 

 duct the duct of the submaxillary gland fills with saliva and a fine 

 cannula is inserted into it. Stimulation of the nerve will cause the 

 saliva to flow very rapidly. The gland is exposed a little behind the 

 posterior angle of the lower jaw bone, and is closely observed before 

 and during stimulation of the chorda. During stimulation of the 

 chorda the gland becomes flushed because of the dilation of its blood 

 vessels, showing the presence of vasodilator nerves in the chorda 

 tympani. 



If the cannula in the duct be attached to a mercury manometer, con- 

 tinued stimulation of the chorda tympani will show that the saliva is 

 secreted from the gland with greater force than that exerted by the 

 arterial blood pressure, as shown by the fact that the manometer 

 attached to the duct will register a greater pressure than that shown 

 by the arterial manometer. This experiment demonstrates the fact 

 that saliva is not filtered from the blood into the salivary tubules. 



B. Action of Secretin on Pancreatic Secretion (see p. 72). 



Through an incision in the linea alba and after applying ligatures, 

 about two feet of small intestine is removed and washed out under 

 the tap. Open it and with a scalpel scrape off the mucous membrane. 

 Macerate the scrapings with 200 c. c. of 0.4 per cent hydrochloric acid 

 and some sand in a mortar. Transfer to a heater and bring to the 

 boiling point. 



While boiling, add weak caustic soda until the reaction is almost 

 neutral, but still faintly acid. Filter through muslin. The resulting 

 extract contains secretin. A cannula is introduced into the main pan- 

 creatic duct. This is done by pulling the duodenum out through the 

 wound and by blunt dissection, separating the main duct from the 

 pancreas. This duct lies in the dog about a finger's breadth above the 

 point where the head of the pancreas leaves the duodenum. A liga- 

 ture is placed under it and the duodenum is opened by an incision 

 along its free border. The cannula is then inserted through the open- 

 ing of the duct in the duodenum, this opening being marked by a 

 papilla. It is then tied in place by means of the previously applied 

 ligature. 



The drops of the secretion, if any, are counted. 20 c. c. of the secretin 

 is injected into the femoral vein. The effect is to produce an increase 

 in the secretion. Also the effect of the injection on the respirations 

 and the blood pressure and pulse should be noted. The injections, 

 using larger amounts if necessary, are repeated. 



