PERFUSION OF THE MAMMALIAN HEART 209 



upper end of the warmer with rubber tubing through the wall of 

 which is inserted the needle of a small hypodermic syringe con 

 taining the solution. For more continuous addition of greater 

 dilutions of the foreign solution the side tube may be connected with 

 a burette. In Gunn's apparatus a Y tube is provided for these 

 operations. By thus injecting the foreign solution at a distance 

 from the heart it is mixed thoroughly with the perfusion fluid and 

 is properly warmed before the heart is reached. Observations should 

 be made using first of all a few c.c. of a 1% solution of calcium 

 chloride. When the beat becomes very small and the ventricle is 

 almost in calcium rigor (see p. 70) inject a few cc. of a 1% solution of 

 KC1. If the beat does not become restored to the normal in a few 

 minutes or so, inject a little more KC1 solution. Then add still 

 more KC1 until the heart again almost comes to a standstill (in 

 diastole, p. 57), when it may again be restored by injecting CaCLj 

 solution.* It is, of course, evident that this observation does not 

 in itself prove that the two cathions are mutually antagonistic to 

 each other. To prove this it would be necessary to show that 

 without the addition of the antagonistic cathion the beat is much 

 more slowly restored. 



4. The effect of alteration of the H-ion concentration of the 

 perfusion fluid. This is done by cautiously adding, by the above 

 procedure, 0.9 per cent, solution of NaCl containing either some 

 HC1 or some NaOH. 



5. The effect of epinephrin. For this purpose about 1 c.c. of a 

 0.002 per cent, solution of adrenalin chloride solution should give 

 definite results. 



6. The effect produced by applying a tetanising electric current 

 to the ventricle. Whenever the fibrillation becomes marked dis- 

 continue the stimulation and see whether the normal beat becomes 

 restored by continuing the perfusion. Observe carefully the be- 

 haviour of the auricles. 



It is usually necessary to employ more than one heart for all 

 of the above observations. Sometimes, however, all can be done 

 on one preparation. 



*It is not possible to state precisely what amount of the two solutions should 

 be used, because this will vary with the rate of the main perfusion. It may be 

 necessary to repeat the observations several times before the effects are obtained. 



