164 PRACTICAL PHYSIOLOGY 



CHAPTER XL. (Advanced). 

 VASO-MOTOR SYSTEM. 



Innervation of the Blood-vessels. Pith the cerebrum of a large 

 frog and plug the hole with a blunt-pointed match to prevent haemo- 

 rrhage. Curarise the frog lightly, place it on the cork board provided 

 for studying the circulation in the web. Tie out the toes so as to 

 spread the web over the hole in the board. Observe the rate of 

 circulation. Next pass a pin through the occipito-vertebral membrane 

 and destroy the spinal bulb. The circulation will become more rapid 

 owing to dilatation of the arteries. 



Now remove the frog from the board and expose the heart. Suspend 

 the frog in the vertical head-up position. Note that the heart and 

 large vessels are filled with blood. Pass a blanket-pin down the 

 vertebral canal and destroy the spinal cord. The heart and vessels 

 will soon become bloodless owing to the loss of vaso-motor tone. The 

 blood sinks into the dilated abdominal vessels under the influence of 

 gravity. 



Perfusion of Frog's Blood-vessels. Destroy the brain and plug the 

 hole in the skull. Expose the heart. Tie one aorta. Place a ligature 

 under the other, snip it with sharp scissors, and allow the blood to 

 escape. Insert a fine-glass cannula into it pointing away from the 

 heart. Fill the cannula with normal saline by means of a capillary 

 pipette. Connect a rubber tube to a glass funnel and clip the tube. 

 Fill the funnel and tube with Ringer's fluid. Connect the tube with 

 the cannula. No air bubbles must be introduced. Snip the sinus 

 venosus and open the clip. Hang the frog in the vertical position. 

 The fluid circulates, runs out of the sinus, and drops from the toes of 

 the frog into a measure glass. Measure the outflow per minute. 

 Circulate Ringer's fluid plus 1 in 1000 sodium nitrate; the outflow is 

 increased owing to vaso-dilatation. Supra-renal extract produces the 

 contrary effect. 



