10 EXEKCISE II 



III. The heart thus freed is gently Hfted from the chest and placed on 

 the cork plate in the cold Ringer-Locke fluid. Gently wash away clots which 

 adhere. Find stump of superior cava and, holding it open with fine forceps, 

 direct into it a stream of cold Ringer-Locke fluid from the wash -bottle and 

 wash out blood from inside heart chambers. 



Loosen clamp on tube from reservoir in the perfusion apparatus and allow 

 the perfusion fluid (Ringer-Locke) to dribble slowly from the heart cannula (h, 

 text-fig. 6). Slip round the aortic stump the noose of an untied ligature ready for 

 tightening. Seizing firmly with the fine forceps the cut edge of the aorta above 

 the thread-noose, and supporting the weight of the heart with the other hand, 

 bring the heart to the perfusion cannula and draw the aorta over the cannula 

 nozzle. Get your colleague now to tighten the ligature round the aorta on the 

 neck of the cannula, and to secure it. See that the lower end of the cannula lies 

 well above the commencement of the coronary arteries. Take care that no air- 

 bubbles are included in the aorta or cannula in the making of this conn exion. 

 If the ventral aspect of the heart is not towards you when the organ hangs 

 suspended on cannula, turn the aorta on the cannula so as to bring the 

 ventral face of ventricles to the front. 



Note whether the coronary vessels still contain blood or are now washed 

 clear with Ringer-Locke fluid. Note the temperature (t, text-fig. 6, 2) of the 

 inflowing fluid and what quantity is passing through the heart. 



Pass a fine needle carrying a thread with split shot through apex of left 

 ventricle (text-fig. 6, 3). Remove needle, leaving thread, and by the thread 

 secure apex of heart to the horizontal rod below it (text-fig. 6), thus s toadying 

 the suspended organ. 



Steadying the heart with the left hand, attach a pin-hook through the 

 visceral pericardium half-way up right ventricle. Attach the fine thread from 

 the pin-hook in right ventricle to a writing lever arranged for recording beat 

 on drum (text-fig. 6). 



Q Q IV. The heart is probably by this time beating. Inspect the heart's 



Influence of action and take records of it. Count the frequency of the beat. Note the 

 temperature temperature of the perfusion fluid. Bring temperature to 37° C. by arranging 

 the clamp controlling the flow through jacket from the pail (w, text-fig. 6) 

 of hot water. Lower temperature as far as possible and record effect on 



beat-rate.*^ 



Heighten temperature up to but not beyond 42° C. : record the pro- 

 gressive change in beat-rate. 



Reduce the temperature to about 30° C. again. 



on beat. 



