THE EROG, AND OH THE ACTION OE THE TAGUS NERVE. 
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contracts the curve registers not the amount of fluid thrown out by that contraction, but 
the difference between that amount and the amount which has flowed into the auricles 
during- the time of that contraction ; and this latter amount will depend upon the 
extent to which the auricles have completed their relaxation when the ventricle begins 
to contract. It seemed to me, therefore, impossible to come to any satisfactory conclu¬ 
sions when auricles and ventricle were both beating. In consequence, I have attempted 
to prevent the auricles from beating by raising the pressure of the blood solution 
flowing into them sufficiently high, and as Roy* has asserted that a pressure of 
15 centims. is almost sufficient to prevent their contracting, I have always used 
a higher pressure than this, and have always carefully observed that there were no 
movements of the auricles visible to the naked eye or registered on the tracing before 
I proceeded to stimulate the vagus nerve. In this way I have seen most distinct 
relaxation of the ventricle upon vagus stimulation without any slowing of the rate 
of rhythm. Thus Plate 70, figs. 25 A and B, represents two cases taken from the 
same heart as fig. 24 ; the pressure within the auricles was 28 and 29 centims. of 
water respectively, and as is seen by the gradual slope of the curve in fig. 25 B as a 
whole, there was a slight amount of leakage from some part in consequence of the 
high pressure; still the curves show clearly enough that the contractions which occur 
when the nerve is stimulated start from a lower level of the lever ; and as no variations 
in the condition of the auricles was to be noticed, it seems to me that the only 
explanation of such curves as these is that the vagus causes a true relaxation of the 
muscular tissue of the ventricle, and in all probability of the auricles as w r ell. 
If, now, we turn to the consideration of the curves obtained by the method of suspending the heart, we 
see decided indications of the same fact; in many of the carves it can be noticed that with the diminution 
of the beats caused by vagus stimulation, the diastolic line formed by joining the points of greatest 
relaxation falls very slightly nearer to the abscissa than before the stimulation (Plate 69, figs. 15 ,17 A, &c.). 
Another peculiarity can be seen in many of these curves, which is sometimes much more pronounced 
than at other times, viz.: that with the increase in the force of the contractions, the diastolic line is raised 
higher above the abscissa; this is well shown in Plates 68, 69, figs. 10 and 17 A. This diminution of 
relaxation between the beats may be due to an increased tonicity of the ventricle, coincident with the 
increase in the force of the contractions, or it may be caused mechanically by the arrangement of the 
apparatus. Thus, when the clamp is not very tight the movements of both auricle and ventricle are 
transmitted mechanically through the clamp to the other side, so that the contraction of the ventricle not 
only pulls the lower lever upwards but also slightly moves the upper lever downwards, and the reverse 
with the contractions of the auricles; therefore, if the ventricular contraction comes before the auricular 
lever has reached its lowest position of relaxation, then the pull of the ventricle will not only prevent 
the auricular lever falling any lower but will also increase the size of the next auricular contraction. 
This mechanical influence of the ventricular contractions is seen in such cases as Plate 68, fig. 14, where 
the ventricular beats have produced the appearance of strong and weak beats in the auricular curve. 
It is possible then to explain the rise in the diastolic line, both of auricles and ventricle, which 
often occurs after stimulation of the vagus nerve by the fact that owing to the increase in the force of 
the contractions, a stronger mechanical effect is produced upon the contractions of that part of the heart 
* Op. cit., p. 469. 
