EXPERIMENTAL PHYSIOLOGY 



been isolated for a short distance, taking care to avoid injuring it, a 

 thread is tied tightly round it : this serves to hold it, and also severs 

 the continuity of its fibres, and is therefore equivalent to cutting it 

 across, (a) Stimulate the end below the ligature. Observe the effect 

 on blood-pressure caused by cardiac inhibition. (6) Stimulate the 



upper end. Observe the re- 

 flex effects on blood-pressure 

 and on respiration which are 

 produced, (c) Stimulate the 

 superior laryngeal branch, 

 which can be seen passing 

 to the larynx. Observe the 

 effect on respiration and 

 blood-pressure. 



4. Effect of cutting both 

 vagi. The ligature of the 

 one vagus which, as just 

 explained, severs its fibres 

 produces little or no effect 

 on blood-pressure or respira- 

 tion. Now tie or cut the 

 other vagus also. Notice the 

 effect, if any (a) on respira- 

 tion, (6) on blood pressure. 

 Repeat the excitation experi- 

 ments. 



5. Inject solution of atro- 

 pine sulphate (about 2 milli- 

 grammes) into the jugular 



FIG. 73. -Cannula for insertion in the pulmon- vein Notice the effect, if 

 ary artery through the wall of the right ,-. -, 



ventricle, (a) Open end of cannula with an J' u P on blood-pressure and 

 plug of Chatterton's cement attached to respiration. Repeat the ex- 

 wire passing through cork, d; b, lateral citation of lower and upper 

 tube for connecting with recording appar- ends of vagus as in (1), and 

 atus ; c, wash-out tube. note resultSi 



6. If a rabbit is used, 



two other very fine nerves can be found in the neck accompanying the 

 carotid artery and vagus. One of these is the depressor : it is a branch 

 of the vagus or of the superior laryngeal. The other is the cervical 

 sympathetic : it passes above into the superior ganglion. Both these 

 nerves are to be tied low down. After tying the sympathetic, the 

 pupil of the eye on that side will be more contracted than the other, 

 the third eyelid will be partly drawn over the globe, and the ear of 



