PERFUSION OF HEART 77 



The beats will recommence, either spontaneously or in response to 

 stimulation, the normal character being resumed. If the potassium 

 salt is added in excess the heart will be arrested in diastole. 



Perfusion of the heart in situ Tait's method (Fig. 64). The 

 heart can be perfused in situ by introducing a glass cannula into the 

 sinus venosus through the inferior vena cava. The cannula is provided 

 with a vertical tube about 4 centimetres long, and is fixed to the frog- 

 cork by a clamp, or by a cork and pins. This vertical tube is left 

 open : it serves the double purpose of trapping air-bubbles which might 

 pass into the heart, and of preventing the pressure of the supplying 

 fluid from rising too high. The cannula is connected with a bottle 

 of Ringer's fluid, which is allowed to drop very slowly from its fine 

 end during insertion into the vein. It is then tied in, and the 

 heart, previously exposed and attached to a heart lever (as in Fig. 64), 

 is flushed with the solution, which is allowed to flow out from a cut in 

 the aorta. Drugs are introduced either by means of a second bottle, 

 as in Fig. 63, or by introducing them into the cannula through the 

 vertical tube by a small syringe or capillary pipette. 



Perfusion of the mammalian heart. The heart is excised from a 

 recently killed cat or rabbit, and the aorta is at once tied on to a 

 cannula through which Ringer's solution, saturated with oxygen, 

 is slowly dropping. The solution is warmed to about 38 C. before 

 reaching the heart which is itself kept in a warmed chamber. The 

 cannula is directed towards the aortic valves, which are closed on 

 raising the pressure of the perfused fluid; this runs through the 

 coronary vessels and escapes through the right auricle. The amount 

 of fluid perfused can be measured by a tilter (see Fig. 80). The con- 

 tractions of the heart are recorded by one or more light levers, attached 

 to it by threads which are passed round pulleys. The action of drugs 

 is investigated by adding them to the Ringer's solution : the best plan 

 is to inject them with a hypodermic syringe passed through the rubber 

 tubing which conducts the Ringer's fluid to the heart. 



For perfusion of the mammalian heart, Ringer's fluid containing 

 0*9 per cent. NaCl must be used. It may contain, besides the in- 

 gredients given on p. 2, a certain amount of pure gum arabic 

 (Bayliss). 



