VASOCONSTRICTION AND CERVICAL SYMPATHETIC 105 



Faradize for 5" the head end of the cut left sympathetic. The fine 

 arteries as seen from the front surface of the left pinna will shrink and 

 become almost invisible. After cessation of the stimulation they will 

 reappear. 



Repeat the faradization, this time stimulating for 10". Note that, as 

 observed from the back of the pinna by transmitted light, the central artery 

 becomes smaller, the connecting vessels between it and the marginal vein 

 will shrink and many of them disappear, but the marginal vein will still 

 remain easily seen (PI. V, fig. 7). The connecting vessels will begin to reappear 

 about 3" after cessation of the stimulation. 



IV. Place the decerebrate carcase on the weighing-scales and note 

 its weight. 



V. Have ready (1) a 100 c.c. beaker and glass rod for whipping the 

 blood ; (2) 4 clean test-tubes and 4 conical centrifuge-tubes, in a rack, also 

 5 c.c. of 25 per cent, potassium oxalate solution and a small pipette ; (3) an 

 arterial cannula with curved shank and with 10 cm. of rubber tubing attached ; 

 (4) a small evaporating-dish ; (5) 100 c.c. of gum-saline solution (Bayliss's fluid) 

 in a beaker, and a syringe, of 25 c.c. capacity or more : the rubber on cannula 

 should fit the nozzle of this syringe ; (6) two small test-tubes supported 

 by wire in a 100 c.c. beaker, which serves as a water-bath for them ; the beaker 

 stands on a wdre-gauze-covered tripod over a small Bunsen burner or 

 spirit-lamp ; a thermometer in the beaker. 



Get ready mercury manometer, cannula, and kymograph for a 

 carotid-pressure observation as in previous exercises, except that manometer 

 should be set for a pressure commencing at about 120 mm. Hg. 



Place with the tube-pipette 5 drops of the pot. oxalate solution at the 

 bottom of each of the centrifuge-tubes. 



VI. Operation. Place preparation supine, with limbs symmetrically 

 extended. Abduct one knee with clip-weight (PI. IX, fig. 6), and in that 

 thigh expose the distal part of ext. iliac artery and the top of the femoral, 

 and place 3 thread loops, the middle at top of the groin, in readiness for 

 insertion of cannula into femoral. Replace the skin over the wound. 



VII. Proceed to a carotid-pressure record as in previous exercises, e. g. 

 exerc. V. After a sample graphic stop the kymograph. 



