LXIII.] 



CAPILLARY BLOOD-PRESSURE. 



303 



The vagus should also be isolated and ligatured as if for experiment. It is 

 well to use shielded electrodes, such as are shown in fig. 227, The vagus ia 

 tied and divided, and if its peripheral 

 end is to be stimulated, the peri- 

 pheral end is drawn through the 

 shielded electrodes, which are then 

 connected with the secondary coil of 

 an induction machine. To complete 

 the arrangements, an induction 

 machine ought to be set up. 



(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 intrt)duce a suitable glass cannula 

 with a short piece of india-rubber 

 tubing tied on to it. Place another 

 ligature round the arterv, 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 

 clockwork going ; if one were operating on a living animal, the next thing to 

 do would be to remove the clamp or forceps between the cannula in the 

 artery and the heart. At once tlie swimmer would begin to move and record 

 its oscillations on the paper moving in 

 front of it. 



{d.) Before joining the lead tube to 

 the cannula, isolate the vagus, the 

 largest of the three nerves ; put a liga- 

 ture 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 ft'om the sympa- 

 thetic, 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 (fig. 226). 

 Moreover, if the sympathetic be traced upwards, a ganglion will be found on 

 it. This is merely to be regarded as an exercise for practice. 



Fig. 226.— Nerves In the Neck of the Rabbit. 

 a. Sympathetic ; 6. Hypoglossal, with c, 

 its descending branch (descendens noni) ; 



d. Branch of a cervical nerve joining e ; 



e. Vagus, with /, its superior laryngeal 

 branch ; g and h. The origins of the supe- 

 rior cardiac or depressor nerve. 



\asL?sy 



Fig. 227.— Forms of Shielded Electrode! 

 for Stimulating the Vagus or a Deeply- 

 Seated Nerve. 



