302 



PRACTICAL PHYSIOLOGY. 



[LXIII. 



manometer is filled by means of a syringe with a saturated solution of sodium 

 carbonate as high as the stem of the T-piece. To it is attached a long india- 

 rubber tube, which is connected with a pressure-bottle filled with a saturated 

 solution of sodium carbonate, and kept in position by a cord passing over a 

 pulley fixed in the roof. A clamp compresses the india-rubber tube just 

 above the manometer. Open this clamp and also the one at the end of the 

 lead pipe. The alkaline solution fills the whole system, and after it does 



so, and no air-bubbles are present, 

 close the clamp at the end of the 

 lead tube, and then the one on the 

 pressure-bottle tube. It is well to 

 have an inch or more of positive 

 pressure in the manometer. See 

 that the writing-style writes smooth- 

 ly on the paper, and that it is kept 

 in contact with the latter by a silk 

 thread with a shot attached to its 

 lower end. 



B. Insert the Cannula. (.) 

 Arrange the necessary instruments 

 in order on a tray scissors, scalpels, 

 forceps (coarse and fine), seeker, 

 well-waxed ligatures, small aneurism 

 needle, bull-dog forceps, cannulae, 

 sponges. 



(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. The dissection is 

 made below the level of the larynx. 

 Lying just external to the carotid 



is the vagus. " After raising the carotid, under it, and internal to the vagus, 

 are seen two fine nerves ; the more internal and finer one is the depressor 

 or superior cardiac branch of the vagus (fig. 226), the other is the sympathetic. 

 Note that the smallest of the three nerves is the depressor, which is easily 

 isolated from the sympathetic by means of a seeker. If in doubt, trace 

 the sympathetic upwards until it merges into the large swelling of the 

 superior cervical sympathetic ganglion. The depressor should be tied low 

 down in the neck and divided below the ligature, as if for an experiment on 

 its function. It is an afferent nerve, and therefore its central end must be 

 stimulated. 



FIG. 225. Simple Form of Kymograph. On 

 the right is the manometer, the float re- 

 cording the movements of the mercury on 

 a simple revolving cylinder. 



