ELEMENTARY EXPEEIMENTAL PHYSIOLOGY 



97 



(v. Bezold's ganglion), and in the auriculo-ventricular groove 

 (Bidder's ganglion). The nerve cells are the cell stations of the 

 vagus nerve. The nervous system regulates, but does not initiate 

 either the rhythm or sequence of the heart. The maintenance of the 

 rhythm depends on the blood, and there is evidence to show that 

 it especially depends on the oxygen, and on the mineral salts which are 

 in solution in the blood. 



The chief mineral salts, chlorides and phosphates of sodium, potassium, 

 and calcium, are dissolved in the blood in minute traces, and are in a 

 state of ionisation. The presence of these ions seems to be absolutely 

 necessary for the production of the excitatory state. As the mineral 

 salts in the serum, with a due supply of oxygen and water, are 

 sufficient to maintain the heart in rhythmic activity for hours, it is 

 clear that the heart muscle contains a large supply of contractile 

 material in its sarcoplasm. 



CHAPTER XXVI. 



METHODS OF RECORDING THE HEART. 



The Suspension Method of Recording the Heart-beat The frog is 

 placed on a cork plate which is fixed to the stand beneath the lever. 



FIG. 90. -Suspension method of recording the contraction of the frog's heart, with 



use of rubber thread as a spring. 



G 



