THE HEART 83 



effect, it may suffice to add several drops of a 0.9 per cent, solution of 

 potassium chlorid to the saline solution. As soon as the preparation 

 has become quiescent, immerse it in fresh saline solution or in Ringer's 

 fluid, which contains the aforesaid salts in the following proportion: 

 NaCl, 0.7 per cent.; KC1, 0.035 per cent.; CaCl 2 , 0.026 per cent. The 

 rhythm will presently be restored. 



Annotation. With some care a turtle's heart may be made to last throughout 

 these experiments. If it does not, use a frog's heart to complete this series. The 

 action of the salts may also be studied separately upon different hearts. The pre- 

 ceding order, however, should be adhered to, owing to the possibility of saving 

 material. 



Conduction Through the Ventricle. Pith a frog and expose the 

 heart. Destroy the continuity of the nerve-fibers in the ventricle by 

 making four interdigitating cuts across it two cuts starting from its 

 left border and two from its right. Since the wave of contraction 

 nevertheless descends over this zigzag strip, the wave of excitation 

 must be propagated by the muscular elements. 



Separate the ventricle from the auricles by a transverse cut. Note 

 that the latter continue to beat synchronously with the sinus, while the 

 former remains quiescent. Apply the hand-electrodes successively to 

 the base and apex of this zigzag strip of ventricle. Observe that the 

 wave of contraction can thus be made to travel from base to apex as 

 well as in the reverse direction. 



