ESTIMATION OF BLOOD-PRESSURE. 243 



(b.) Make the necessary dissection on a dead rabbit. 

 Fix the rabbit in a Czermak's holder as would be done if 

 the animal were alive. Clip away with a pair of scissors the 

 hair over the neck, and with a moist sponge moisten the 

 skin to prevent any loose hair from flying about. Pinch up 

 the skin on one side of the trachea, between the left thumb 

 and forefinger, and divide it with a sharp scalpel. This 

 exposes the fascia, which is then torn through with forceps, 

 draw the sterno-mastoid aside, and gently separate the 

 muscles with a " seeker " until the carotid, accompanied by 

 the vagus, depressor, and sympathetic nerves is seen. 



(c.) Open the sheath, and with the seeker carefully 

 isolate about an inch of the carotid. Pass a ligature under 

 the artery by means of a fine aneurism needle, withdraw 

 the needle, and ligature the artery. About an inch on the 

 cardiac side of the latter, clamp the artery with bull-dog 

 forceps. Raising the artery slightly by the ligature, with 

 a fine-pointed pair of scissors make an oblique V-shaped 

 slit in the artery, and into it introduce a suitable glass 

 cannula with a short piece of india-rubber tubing tied on 

 to it. Place another ligature round the artery, and tie it 

 round the artery and over the shoulder of the cannula. 

 The point of the cannula is of course directed towards the 

 heart. Fill the cannula with the soda solution, and into 

 the cannula slip the glass nozzle at the end of the lead 

 pipe, tying it in securely. Unscrew the clamp at the end 

 of the elastic tubing. Set the clock-work going; if one 

 were operating on a living animal, the next thing to do 

 would be to remove the clamp or forceps between the artery 

 cannula, and the heart. At once the swimmer would begin 

 to move and record its oscillations on the paper moving in 

 front of it. 



(c?.) Before joining the lead tube to the cannula, isolate 

 the vagus, the largest of the three nerves, put a ligature 

 round it, and divide it above the ligature. Isolate also the 

 depressor nerve, put a ligature round it low down in the 

 neck, and divide it between the ligature and the heart. 

 The latter is easily distinguished from the sympathetic, as it 

 is the smallest of the three nerves accompanying the carotid. 

 In the dead rabbit the depressor may be traced up to its 

 origin by two branches, one from the vagus, and the other 

 from the superior laryngeal. Moreover, if the sympathetic 



