UPON THE VASCULAR SYSTEM. 147 



5th. Although in all the experiments the pulse remained unchanged when 

 the pressure underwent no alteration after division of the vagi, it was variously 

 affected when the pressure was increased. In four cases (see Table III.) it was 

 accelerated, in three it remained unchanged, while in one it was retarded. 

 Seeing that the acceleration in these cases and in those previously given (see 

 page 120) took place when the cardio-inhibitory nerves had been paralysed 

 previous to the section of the vagi, it is certain that it could not be due to 

 escape of the heart from control. To what cause, then, shall we ascribe it ? I 

 can think of none other than a direct influence of the increased blood-pressure 

 upon the lining membrane of the heart. It is now generally agreed that — as 

 Ludwig and Trtry* pointed out — if the vagi have been previously divided, — 

 that is, if the cardio-inhibitory nerves are not in operation, increased blood- 

 pressure usually accelerates and very rarely retards the pulse.t The retardation 

 is commonly the result of an extraordinary increase of the pressure. My expe- 

 riments on this question have convinced me of the truth of the above, but I have, 

 moreover, frequently noticed that a considerable rise in the blood-pressure may 

 take place without causing any change in the rapidity of the heart's action. As 

 these results are all illustrated in Table III., I therefore think that in the first 

 five experiments there recorded, the acceleration and retardation of the pulse 

 were due to the increased blood-pressure. Whether this be or be not the true 

 explanation, it is certain that the acceleration of the pulse which so frequently 

 follows section of the vagi, is not, as is generally supposed, dependent merely on 

 escape of the heart from the influence of its controlling nerves, but depends on at 

 least another cause — and that probably is — a rise in the blood-pressure. Seeing 

 that such is the case, the amount of acceleration of the pulse which may follow 

 division of the vagi, cannot any longer serve as an accurate index to show the 

 extent to which the cardio-inhibitory fibres of the vagi may be in action previous 

 to their section, indeed we have as yet no accurate test by means of which this 

 may be ascertained. It has, indeed, been stated by Von Bezold, that a trust- 

 worthy test is to be found in the action of atropia. Most of my experiments 

 show that when sulphate of atropia is administered previous to division of the 

 vagi, a varying degree of acceleration of the pulse almost always ensues. It 

 has been said by the above-named author^ that this acceleration is entirely due 

 to palsy of the cardio-inhibitory nerves — the heart simply attaining the speed 

 which it would maintain but for the inhibitory action of these nerves. Von 

 Bezold came to this conclusion from observing that atropia never accelerates 



* Wiener, Sitz. Berichte, 1864, Band 49. 



t Much, confusion has been produced by certain authors discussing the influence of the blood- 

 pressure upon the cardiac movements without distinguishing between the influence of the pressure before 

 and after section of the cardio-inhibitory nerves. 



% Von Bezold. Untersuchungen aus dem physiologischen Laboratorium. Wiirzburg, 1867, 

 Erstes Heft. 



VOL. XXVI. PART I. 2 Q 



