118 Dr. J. A. Mc William. The Structure and Rhythm [Jan. 29, 



succession of contractions — in response to the more rapid series of 

 shocks sent into it. In short, the rate of contraction depends on the 

 rate at which the stimulations are applied ; the quicker the series of 

 shocks sent in, the quicker is the series of responsive contractions. 



In the eel's ventricle the phenomena are of a strikingly different 

 nature. For a slowly interrupted current is found to cause a much 

 more rapid series of contractions than does a rapidly interrupted 

 current of precisely equal strength. When a rapidly interrupted 

 current is sent through the quiescent ventricle (of an eel's heart), the 

 rate of contraction induced varies within certain limits according to 

 the strength of the current employed. When a rapidly interrupted 

 current {e.g., sixty shocks per second) is used of such a strength as 

 to cause a slow series of ventricular beats, it is found that a diminution 

 in the rate of interruptions {e.g., to six per second), at once leads to 

 the appearance of a much more rapid series of ventricular beats. The 

 number of contractions resulting from the application of the slowly 

 interrupted current is much greater than that caused by a rapidly 

 interrupted current ; the influence, moreover, of the former is much 

 more lasting than the influence of the latter. A much closer approach 

 to a tetanic condition is induced by a slowly interrupted current than 

 by a rapidly interrupted one. And this statement holds with regard 

 to (1) the ventricle of an intact heart ; (2) the isolated quiescent 

 ventricle; and (3) the isolated automatically-contracting ventricle. 

 It holds also with regard to various rates of interruption in the 

 stimulating currents. A current interrupted ten times a second is 

 much more effective than one interrupted fifty times a second. The 

 rule holds, then, that — within certain limits — a slowly interrupted 

 current, whether galvanic or faradic, produces much more striking 

 effects than a rapidly interrupted one, the influence of the latter 

 being much less powerful, and, at the same time, of a less enduring 

 character. It is not necessary when dealing with a slowly interrupted 

 current that the shocks be sent in at any particular phases of the 

 cardiac beat ; a series of shocks is simply sent in without regard to 

 the state of the organ at the moment when each shock is sent in. 



A very striking difference is also evident in the results obtained by 

 the continued application of a weak interrupted current to the 

 ventricle as compared with the repeated temporary application of the 

 same current. The latter is commonly able to induce a fairly rapid 

 series of ventricular contractions when the former has no apparent 

 effect at all or merely causes a very slow succession of beats. 



These remarkable differences in the effects of interrupted currents 

 are manifested not only in the case of the ventricle, but in the auricle 

 and sinus as well — in all the portions of the cardiac muscle. 



As a result of the application of weak interrupted currents, I have 

 observed no mark jd effect upon the ventricle of the eel's heart. There 



