116 



ning of ventricular contraction and the opening of the aortic 

 valve, as shown by the upstroke in the pulse curve consequent 

 upon the entrance of liquid into the aorta. 



XXXI 



367. Blood Pressure in the Frog. Curarize a frog 

 lightly, and expose the heart with the aortae leading off from 

 it. Get ready a fine cannula with a short piece of rubber tub- 

 ing attached. Fill the tubing and cannula with a 1 per cent 

 solution of Sodium Carbonate and close the end of the tube 

 with a clamp. Dissect out one of the aortae and tie a ligature 

 around it as far as possible from the heart. Pass a second 

 ligature around the same aorta, without tying, nearer to the 

 heart. Lift the aorta with the second ligature and with a 

 pair of sharp pointed scissors make a slight incision in the 

 vessel and introduce the cannula into this incision and tie it 

 with the second ligature. Fill the proximal end of the mano- 

 meter with a 1 per cent solution of Sodium Carbonate seeing 

 that all air is excluded, so that when the tubing is attached 

 to the manometer, there will be a continuous volume of the 

 Sodium Carbonate solution from the cannula to the mercury 

 of the manometer. Before attaching the tubing to the mano- 

 meter, clamp the aorta or have your co-worker compress it 

 carefully with a pair of forceps. Place the frog-board on a 

 wooden stand, so as to bring the heart to a slightly higher 

 level than the level of the mercury in the manometer. Bring 

 the writing point of the lever of the manometer against a 

 smoked drum and revolve the drum once so as to record a line 

 of atmospheric pressure. 



After the cannula in the- aorta, with its tube has been 

 attached to the manometer, remove the clamp of forceps from 

 the aorta and allow the blood from the heart to pump against 

 the Sodium Carbonate and mercury in the manometer. The 

 columns of mercury in the proximal and distal tubes will be 

 no longer at approximately the same level. The mercury in 

 the proximal tube will fall slightly and will rise correspond- 

 ingly in the distal tube. Note that with each beat of the 

 ventricle the column rises a short distance above the mean 



