40 EXERCISE -VI 



cleidal portion combined with the cephalo-humeral muscle is lateral, the 

 sternal is to the median side. Make an antero-posterior incision through the 

 skin from the middle of this space and carry it about 4 cm. forward. 



Retract the edges of the skin wound. Observe the vein and the 

 branches entering it. In a length between two branches pass three 

 ligatures as for an artery. Occlude the vein at its heart end by drawing 

 on the proximal ligature-controlling loop and attaching a small weight 

 to the loop thread-ends. This prevents the vein from emptying and makes 

 the opening of the vein easier. Then tie the distal ligature. - With fine- 

 pointed 'scissors cut obliquely half through the vein 3 mm. distal to the 

 middle^ ligature. Slip the cannula nozzle into the opening in the vein and 

 insert so that neck of nozzle comes under the ligature ; tie the cannula 

 securely in. Fill the cannula with Ringer-Locke from the filler-up. Attach 

 the junctional rubber from manometer to the cannula in the same way as 

 is done in the arterial pressure procedure, your colleague helping you to avoid 

 inclusion of any air by running Ringer-Locke from the filler-up pipette over 

 the junction as it is made. Release the occluding loop as soon as this is 

 done. Observe the pressure and its oscillations ; note the relation of the 

 latter to the puffs of the ventilating-pump. Compare them with those in 

 the arterial-pressure Hg manometer. 



Obs. 26. VIII. Get ready inductorium and circuits and hand-electrodes for 



ec usion of the f^Y^^[Q stimulation. Have at hand two or three fine entomological pins, 

 coronary . . . ... 



arteries on Expose one of the vagi in the neck ; ligate and isolate it for electrical 



heart-beat. stimulation as in exerc. IV, and as in that exercise expose the heart by 



removing part of the front of the chest. 



Note the position of the left and right coronary arteries (PI. I, fig. 4), 

 Faradize the distal stump of the vagus, and while the heart is restrained 

 from beating rapidly pass one of the fine pins under the left coronary 

 vessels, through the cardiac tissue, and as high up the course of the vessels 

 as possible. Directly the pin is inserted cease the stimulation. Repeat 

 the manoeuvre with the right coronary vessels. 



The heart continues to beat as before. Twist a thread tightly round the 

 projecting ends of the left coronary pin so as to occlude the coronary vessels. 

 Note the result. Repeat with the right coronary vessels. 



ANNOTATION 



Ohs. 22. For adrenal extract see Anno- vasoconstriction by acting on the vasomotor 

 tation, exerc. I. Its action on the blood- centre in the bulb is proved by your experi- 

 pressure is ' peripheral ' not ' central ' ; it ment on the decapitate preparation, 

 constricts ; that it does not produce the Ohs. 23. For the effect of asphyxia on 



