.VIKiU 0'ilU))iO'l 



104 



EXERCISE XYII 



INFLUENCE OF CERVICAL SYMPATHETIC ON BLOOD-VESSELS OF THE 

 PINNA. HAEMOERHAGE AND ARTERIAL PRESSURE ; RESTORATIVE 

 EFFECT OF GUM-SALINE INJECTION (BAYLISS). CLOTTING OF BLOOD ; 

 FIBRINOGEN 



I. See that the decerebrate preparation provided is in good 

 condition. 



Obs. 78. 

 Cervical 

 sympathetic 

 and vessels of 

 the pinna. 



II. Get ready the inductorium circuits for faradic stimulation. 



III. Place the preparation supine with all four limbs symmetrically 

 extended. Expose the left cervical sympathetic by a dissection similar to that 

 already described for exposure of the vagus nerve (exerc. lY, PI. II), remember- 

 ing that sympathetic runs along with vagus on the medial side of that 

 nerve, and is much the smaller nerve. Separate the sympathetic from vagus 

 trunk by working with the point of a mounted needle between the two 

 nerves. Pass a ligature round the sympathetic nerve after carefully separating 

 it from the vagus nerve ; the ligature should lie about 15 mm. behind the level 

 of the cricoid cartilage. Tie the ligature. Sever the nerve posterior to 

 the ligature, and dissect the nerve headward for about 2 cm., raising the 

 nerve by the ligature as it is followed headward. 



Eaise the neck-stump of the preparation so that the attached pinnae 

 are easily inspected and in a good light. Observe the condition of the 

 blood-vessels of the skin of the pinnae (PI. V, fig. 6). The observations 

 can be made either by looking at the front concave surface by reflected light 

 or by looking at the convex surface by transmitted light. If the former, 

 note fine diverging vessels (arteries) sloping towards the flattened border 

 of the pinna near the tip. If the latter, shave carefully a piece of the ear- 

 surface, about the size of a sixpence, near the tip. Spread a drop of strong 

 glycerine over the shaved surface, and so place the ear that the light 

 of the window comes through it to the eye ; screen the eye from the window 

 light elsewhere as you look at the pinna. Compare the vascularity of the two 

 pinnae, right and left, in this way. The vascularity of the left, that is of the 

 side on which cervical sympathetic has been cut, will probably be obviously 

 the greater. Feel with the fingers the tips of the two pinnae ; that of the 

 left will probably be perceptibly the warmer. 



