Venous Sinus. 



As regards the relationship of the auricular reduplication to the 

 time of stimulation, we find the latency of the auricle occasionally 

 varying in length, but usually it has very nearly equal values, except 

 when the shock, falling during ventricular relaxation, calls forth a 

 simultaneous auricular and ventricular contraction, and. in this case 

 latency is reduced. It is to be noted that this induced auricular 

 contraction does not cause another induced ventricular systole : its 

 further effects seem to be lost or dissipated. 



At two points in Chart T, ventricular systole being advanced half- 

 way and *6 of the way to its maximum, the auricular latency is equal, 

 and when at the end of ventricular relaxation the auricle contracts at 

 the same time as the ventricle, the latency is still about the same. 

 The time lost, therefore, in this case is in ventricular reduplication : 

 either the impulse from the auricle is transmitted at different speeds 

 at different times, or it meets at different times with variation in the 

 excitability of the ventricle. The later in the systole the stimulation 

 falls the less is the resistance to the transmission of the impulse or 

 the greater the excitability of the ventricle. 



The whole subject of the rhythmical contraction of the frog's heart 

 and its stimulation and inhibition is a very complex and difficult one. 

 The points upon which our present research seems to us to throw 

 some light are the nature and mode of transmission of the stimuli 

 which one cavity transmits to another in the ordinary process of 

 rhythmical contraction. Marey's researches have shown that in the 

 ventricle itself there is a time when stimulation applied to it has no 

 apparent action ; this time is, however, in many cases of very short 

 duration and limited to the commencement of ventricular systole. 

 At the commencement of ventricular systole stimulation without 

 provoking contraction causes often a positive effect, namely, a greatly 

 prolonged diastolic pause, which we have been inclined to regard as 

 due to omission of a ventricular contraction. 



