190 A MANUAL OF PHYSIOLOGY 



both vagi while a tracing is being taken ; the blood-pressure rises still 

 more (p. 475). The rise is not long maintained, but a second injec- 

 tion causes a renewed increase of pressure. 



24. Section and Stimulation of the Cervical Sympathetic in the 

 Rabbit. Weigh out f gramme chloral hydrate. Dissolve in as small 

 a quantity of water as possible, and inject into the rectum of a rabbit, 

 preferably an albino. Half a gramme is sufficient for a small rabbit. 

 Put a pair of bulldog forceps for a few minutes on the anus to pre- 

 vent escape of the solution. Set up an induction coil arranged for 

 an interrupted current (Fig. 65, p. 175), and connect it through a 

 short-circuiting key with electrodes. The preparations necessary for 

 an operation with antiseptic precautions are supposed to have been 

 previously made the instruments, sponges, and ligatures boiled in 

 water ; the instruments then immersed in a 5 per cent, solution of 

 carbolic acid, the sponges and ligatures in corrosive sublimate solu- 

 tion (o'i per cent.). The hands are to be thoroughly washed, with 

 diligent use of the nail-brush, in soap and water before the cutting 

 operation begins, and then soaked in the corrosive sublimate solution. 



Fasten the rabbit on a holder, back downwards, as in Fig. 43. 

 Keep the animal warm by covering it with a cloth, and do not handle 

 or wet its ears. Clip off the hair on the anterior surface of the neck. 

 Remove loose hairs with a wet sponge, shave the neck, and wash it 

 thoroughly, first with soap and water, and then with corrosive 

 sublimate. Give ether if necessary. Make a longitudinal incision 

 in the middle line over the trachea, beginning a little below the 

 thyroid cartilage and extending downwards for an inch and a half. 

 Feel for the carotid artery, expose, and raise it up. Two nerves will 

 now be seen coursing beside the artery. The larger is the vagus, the 

 smaller the sympathetic. A third and much finer nerve (the de- 

 pressor, or superior cardiac branch of the vagus) may also be seen in 

 the same position, but the student should neglect this for the present. 

 Get as little as possible of the antiseptic solutions in the wound till 

 your observations have been completed, as the nerves may be injured 

 by them. Pass a ligature under the sympathetic, and tie it, the 

 ear being held up to the light while this is being done, so that its 

 vessels may be clearly seen. A transient constriction of the arteries 

 may be seen at the moment when the nerve is ligatured. This is 

 due to stimulation of the vaso-constrictor fibres. Then follows a 

 marked dilatation of the bloodvessels, due to paralysis of these fibres. 

 The ear is flushed and hot. Note also that the pupil is probably 

 narrower on the side on which the nerve has been tied. On stimula- 

 tion of the upper (cephalic) end of the sympathetic with the electrodes, 

 the vessels are markedly constricted, the ear becomes pale and 

 cold, and the pupil dilates. Cut the nerve above and below the ligature, 

 and take out the ligature. Wash the wound thoroughly with corrosive 

 sublimate, and close it, the muscles being first brought together by a 

 row of interrupted sutures, and then the skin by another row. Since 

 it is difficult to thoroughly disinfect the hair-follicles, and a suture 

 passed through a septic follicle is apt to give rise to suppuration, sub- 

 cutaneous stitches i.e., stitches passed by a curved needle through 



