492 



Drs. T. L. Brunton and T. Cash. 



It seemed of interest to ascertain whether a similar condition 

 occurred in the other cavities of the frog's heart. We find that in the 

 auricular stimulation about or shortly after the period of maximum 

 contraction of the auricle may cause inhibition of the next auricular 

 beat. 



We have not yet succeeded in registering the contractions of the 

 venous sinus with sufficient accuracy to enable us positively to deter- 

 mine the occurrence of a similar refractory period in the venous sinus 

 itself, but the results we have obtained lead us to hope that we shall 

 soon be able to do so. 



Another interesting consideration is, whether the stimulus which 

 each cavity of the heart transmits to the succeeding one, consists in the 

 propagation of an actual muscular wave, or in the propagation of an 

 impulse along the nerves. The observations of Gaskell have given 

 very great importance to the muscular wave occurring in each cavity 

 of the heart of cold-blooded animals as a stimulus to the contraction 

 of the next succeeding cavity. Our observations appear to us to 

 show that while this is an important factor, it is not the only one in 

 the transmission o'f stimuli. We have observed that stimulation of 

 the auricle rarely or never causes contraction of the ventricle unless the 

 auricle also contracts. When stimulation of the auricle causes both 

 itself and the ventricle to contract, the auricular contraction precedes 

 the ventricular one in such a way that we might be justified in 

 regarding the ventricular contraction as due to the propagation of 

 the contractile wave from the auricle to the ventricle. It would also 

 appear that a contractile wave may be propagated backwards, for on 

 stimulation of the ventricle we have observed the contraction of the 

 ventricle produced by stimulation has been succeeded by an auricular 

 contraction such as might be supposed to be due to propagation of 

 the contractile wave back from the ventricle to the auricle. While 

 these observations appear to show that the propagation of the con- 

 tractile wave from one cavity of the heart to another is of importance 

 in keeping up the rhythmical sequence, we consider that stimuli are 

 also propagated from one chamber of the heart to another through 

 nervous channels : — thus we find that irritation of the venous sinus 

 will sometimes produce simultaneous contractions of the auricle and 

 ventricle, instead of the ventricular beat succeeding the auricular in 

 the usual way. This we think is hardly consistent with the hypothesis 

 that a stimulus consists of the propagation of a muscular wave only 

 from the auricle to the ventricle. 



As additional evidence we may notice the occurrence of an auricular 

 beat followed by absence or inhibition of a ventricular beat as the 

 result of stimulation of the auricle, or venous sinus. Moreover, we 

 have noticed in the heated heart the occurrence of groups of regular 

 beats in the ventricle in consequence of a single stimulation applied 



