210 



THE CIRCULATION OF THE BLOOD AND LYMPH 



trace a curve showing an elevation for each heart-beat, and longei 

 waves due to the movements of respiration. 



(b) Isolate the vago-sympathetic nerve 

 in the neck. Ligature doubly, and cut 

 between the ligatures. Stimulate the peri- 

 pheral (lower) end ; the heart will be slowed 

 or stopped, and the blood-pressure will fall, 

 Stimulate the central (upper) end; there 

 may be inhibition of the heart or accelera- 

 tion, and the pressure may fall or rise 

 (p. 168). 



(c) Expose and divide the other vago- 

 sympathetic while a tracing is being taken. 

 Again stimulate the central end of the 

 nerve and observe whether there is any 

 effect. 



(d) Expose the sciatic nerve in one leg, 

 as follows : The leg having been loosened 

 from the holder, the foot is seized by one 

 hand and lifted straight up, so as to put 



Fig. 103. Three-way Cannula. 



the skin of the thigh on the stretch. An 

 incision is now made in the middle line on 

 the posterior aspect of the thigh, through 

 the skin and subcutaneous tissue. The 

 muscles are separated in the line of the 

 incision with the fingers, and the sciatic 

 nerve comes into view lying deeply be- 

 tween them. Place a double ligature on it, 

 and divide between the ligatures. Stimu- 

 late the upper (central end) ; the blood- 

 pressure probably rises, and the heart may 

 be accelerated. Stimulate the peripheral 

 end of the nerve ; there is little change in 

 the blood-pressure and none in the rate of 

 the heart. 



(e) Note, incidentally, that stimulation 

 of the central end of the sciatic or the upper 

 (cephalic) end of the vago-sympathetic 

 may cause increase in the rate and depth of the respiratory movements. 

 Dilatation of the pupil is also caused by stimulation of the upper end of 



Fig. 104. Manometer with 

 Side-tube (Guthrie). A, float ; 

 B, collar through which the 

 wire C of the float moves; D, 

 vertical wire fixed to mano- 

 meter-holder, which keeps the 

 writing-point on the drum; 

 E, limb of manometer con- 

 nected with cannula, with its 

 side-piece, F. 



I 



