PECULIARITIES OF THE CARDIAC MUSCLE. 191 



heart the wave of contraction must travel always in one direction, for 

 all the parts immediately in the rear of the part which is contracting 

 are blocked (being in the inexcitable phase), so that no backward wave 

 is possible. 



The experiments of Bowditch, 1 Kronecker, 2 and v. Basch 3 have 

 shown that a series of single induction shocks, sent in to the muscle 

 of the frog's ventricle, are able to produce an infallible response to each 

 shock only when they are sent in at a slow rate — two seconds being the 

 limit — and that if they are sent in at a quicker rate than this, then 

 a contraction occurs only with every second stimulus. In fact, whether 

 the contraction be due to the travelling of a contraction wave, or to. 

 a direct external stimulus, it will not take place unless sufficient time 

 be allowed for the tissue to recover its conductivity or excitability 

 respectively after a previous contraction. 



From these experiments of Kronecker and v. Basch, combined with 

 my experiments upon the blocking of contraction waves, we see that 

 very similar laws apply to the recovery of excitability and the 

 recovery of conductivity after a contraction, and it makes no difference 

 at any spot whether that contraction is the natural contraction due to the 

 normal beating of the heart, or an artificial contraction induced by an 

 interpolated stimulus between the natural contractions ; just as such 

 stimulus cannot cause a contraction in the ventricle unless it be applied 

 a sufficient time after the commencement of the natural contraction, 

 so also the normal contraction will be blocked if it reaches the ventricle 

 before the tissue has had time to sufficiently recover its conductivity 

 after the commencement of the interpolated or forced contraction. For 

 this reason it is self-evident that an interpolated contraction of the ventricle 

 in the case of a normally beating heart may be followed by a longer 

 pause than usual, because the normal contraction following the beat of 

 the auricle, which ought to take place during that pause, cannot take 

 place, as it arrives during the inexcitable phase of the interpolated 

 contraction. This lengthened pause has been called the " compensatory 

 pause," and attempts have been made to look upon it as an inhibitory 

 phenomenon. It is, however, so clearly due to a blocking of the 

 natural contraction wave by the interpolated contraction, owing to the 

 existence of the refractory period, that it is not necessary to discuss it 

 further. 



In connection with the observations of Kronecker 4 and v. Basch, 5 

 upon the effects of sending in single induction shocks to the cardiac 

 muscle at definite intervals, are observations of v. Basch upon the effect 

 of sending in single induction shocks, the strength of each one of which 

 is insufficient to cause a contraction. He finds that such stimuli will 

 produce a rhythmical series of contractions, the rate of which is less 

 than the rate at which these insufficient stimuli are sent in. The 

 explanation appears to be 6 that a stimulus which is insufficient to cause 

 a contraction increases the excitability of the muscle, and so enables a 

 second or third stimulus of the same strength to be powerful enough to 

 cause a contraction. This observation of v. Basch is in accordance with 



1 Ber. d. k. Sachs. Gesellsch. d. Wnsensch., Leipzig, 1871. 



2 "Das cliaract. Merkmal d. Herzmuskelbeweg.," Bcitr. ~. Anot. v. /'/nisi,,/, n/s 

 Fcstyabe C. Ludwig, Leipzig, 1874. 



s Sitzwngsb. <L jfc. Akad. d. Wissensch., Wien, Bd. lxxix. 



' Op. cit. •' Op. cit. 



u v. Basch, Arch./. Physiol., Leipzig, 1880, S. 283. 



