CHAPTER XXVII. 



PERFUSION OF THE EXCISED MAMMALIAN HEART. 



If a solution containing certain of the inorganic constituents 

 of blood plasma and saturated with oxygen gas be perfused under 

 a certain pressure through the coronary arteries, the heart will 

 beat with perfect regularity for several hours outside the body. 

 This surviving heart preparation is particularly useful for investiga- 

 tions of the influence on the heart of variations in the saline con- 

 stituents of the nutrient fluid and of the effect of drugs. The nutrient 

 fluid is caused to circulate through the coronary arteries by intro- 

 ducing it into the aorta, where it closes the semilunar valves and 

 is forced into the openings of these arteries. The observation also 

 demonstrates most convincingly the remarkable recuperative 

 power of the heart, and it affords evidence that resuscitation 

 methods should be persistently applied after drowning accidents 

 and when death has occurred from other forms of suffocation. 



The most convenient apparatus to use is that depicted in Fig. 63. The per- 

 fusion fluid (Ringer-Locke's or Tyrode's) is contained in the bottle A, and it is 

 kept constantly saturated with pure oxygen by bubbling the gas through it. 

 The fluid then passes to the cannula in the aorta through a warming device which 

 consists of a wide tube surrounded by a water jacket kept at the desired tempera- 

 ture by a thermo-siphon system, as shown in the diagram. In order that the 

 fluid may be thoroughly warmed it is caused to flow in a thin film on the walls of 

 the tube (B) by placing in this a somewhat smaller tube (C) closed at both ends. 

 Although it is convenient to use an apparatus in which the free end of the cannula 

 is ground on its outer surface so as to fit the lower end of the inner tube of the 

 warmer an apparatus devised by the late T. G. Brodie the simpler apparatus 

 devised by Gunn, which is also shown in the figure, is perfectly satisfactory. 

 In Brodie's apparatus a thermometer (T) is inserted into the aortic cannula 

 through a side tube; in Gunn's apparatus the thermometer is made to serve as the 

 inner tube of the warmer. 



The heart is prepared for perfusion as follows: A rabbit is killed by a blow 

 on the back of the head and is immediately laid supine on the table. A longi- 

 tudinal incision is made through the skin of the thorax, extending for a short 

 distance on the abdomen. The skin is retracted to both sides of the incision 

 and the abdomen opened at its upper end. One blade of a stout pair of scissors 

 is then passed through the diaphragm under the cartilages of the ribs on one side 



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