PRACTICAL EXERCISES 



425 



fully slipped on the end of the cannula. The lingual is now to be 

 lifted by means of the ligature, and traced back towards the jaw till 

 its chorda tympani branch is seen coming off and running backwards 

 along the duct. The chor do -lingual nerve (Fig. 143, p. 362) is then 

 to be cut centrally to the origin of the chorda tympani, which can 

 now be easily laid on electrodes by means of the ligature on the 

 lingual. On stimulating the chorda, the flow of saliva through the 

 cannula will be increased. The current need not be very strong. If 

 the flow stops after a short time, it can be again caused by renewed 

 stimulation after a brief rest. A quantity of saliva may thus be 

 collected, and the experiments already made with human saliva 

 repeated. 



(2) Expose the vago-sympathetic nerve in the neck on the same 

 side ; ligature it ; divide below the ligature ; and note the effect 

 produced by stimulation of the upper end on the flow of saliva. 



Submaxillary 

 Gland. 



Digastric 

 Muscle (cut). 



Hypoglossal 



Mylo-hyoid 

 Muscle (cut). 



Lingual Wharton's 

 Nerve. Duct. 



FIG. 157. DISSECTION FOR STIMULATION OF CHORDA TYMPANI (AFTER 

 BERNARD). 



(3) Set up another induction-machine, and connect it with elec- 

 trodes. Stimulate the chorda, and note the rate of flow of the 

 saliva. Then, while the chorda is still being excited, stimulate the 

 vago-sympathetic, and observe the effect. If the experiment is 

 successful, finish by stimulating the chorda for a long time. Then 

 harden both submaxillary glands in absolute alcohol, make sections, 

 stain with carmine, and compare them. 



3. Effect of Drugs on the Secretion of Saliva. (i) Proceed as in 

 2(1), but, in addition, insert a cannula into the femoral vein (p. 200). 

 On the cannula put a short piece of rubber tubing, filled with 0-9 per 

 cent, salt solution and closed by a small clamp, or a small piece of 

 glass rod, or a pair of bulldog forceps. While the chorda is being 

 stimulated inject into the vein 10 to 15 milligrammes of sulphate 

 of atropine by pushing the needle of a hypodermic syringe through 

 the rubber tube. This will stop the flow of saliva, and abolish the 



