90 EXERCISE XIV 



VII. To dissociate these two effects give atropine intravenously 

 (for method and dose see exerc. V, p. 81). 



Repeat the stimulations of § VI. If the fall of arterial pressure 

 obtained by stimulation of the depressor in J V has been complicated by 

 cardiac inhibition, repeat also the stimulations of that section. 



Obs. 71. VIII. Expose the peroneal nerve at outer side of one knee. 



Vasopressor Operation. Lay the preparation on its side with the hind-limb on which 



the nerve is to be exposed uppermost and extended at knee by a weight 

 attached to foot. Make out through the skin the head of fibula and the 

 posterior border of the biceps muscle running over outer side of top of calf. 

 About 1 cm. in front of posterior edge of biceps, and parallel with it, make 

 a 5 cm. skin incision, starting above about level of fibular head, but 

 well behind it. The thin biceps muscle is then seen and through it the 

 peroneal nerve-trunk running deep to and parallel with the muscle's 

 fibres. Cut down to it. Ligate it at distal end of wound, sever distal to 

 ligature, and free it for 3 cm., raising it by the thread of ligature. The 

 operation involves no bleeding. Faradize the raised central end. Observe 

 the blood-pressure record ; it rises in result of this stimulus (text-fig. 34:). 



ANNOTATION 



Obs. 68. Repeats on the cat the discovery, branch, which are exceptions, exerting de- 

 made by E. de Cyon and C. Ludwig, 1865, pressor effect on the mean arterial pressure. 

 JBer. d. Sachs. Gesellsch.d. Wiss.,Math.-Phys. When stimulation of the central end of the 

 CI. 307, in the rabbit, that an afferent nerve vagus trunk below the superior laryngeal 

 • passing from the heart (aorta) to the bulb by causes some rise of arterial pressure before 

 way of the vagus nerve causes a reflex lower- the fall ensues, this pressor effect is due 

 ing of the arterial pressure. It does so by (Fran9ois-Franck, Marey's Travaux de Ldbo- 

 lessening the vasoconstrictive tone exerted ratoire, Paris, p. 340, 1879) to fibres entering 

 by the vasomotor centre in the bulb upon the trunk from its inferior (recurrent) laryn- 

 the arterial system both visceral and cutane- geal branch, and also (Neuman, Jnl. of 

 ous, W. M. Bayliss, 1893 {Jnl. of Physiol. Physiol, vol. xlix, p. 34, 1915) from the 

 xiv. 303 ; Principles of General Physiology, stomach and intestine. In the cat most of 

 p. 694, London, 2nd ed. 1918). the afferent fibres in recurrent laryngeal are 



Obs. 71. The peroneal here typifies the derived from the superior laryngeal by 



effect of most afferent nerves on the blood- peripheral anastomosis of the inferior laryn- 



pressure. It is the vagus trunk (below its geal with the superior in the laryngeal 



superior, and still more below also its inferior, region, the so-called ^ anastomosis of Galen '. 

 laryngeal branch), and especially its depressor 



