BY DR. BURDON-S ANDERSON. 277 



1. The arrest of the heart may be regarded as a result of 

 the excitation of the ganglion of the septum, i. e., the mechani- 

 cal irritation of that part produced by the scissors or ligature ; 

 in other words, as an effect of the same nature as that pro- 

 duced in experiment 4, where that centre is subjected directly 

 to electrical stimulation ; or, 



2. It is dependent on the severance of the sinus vcnosus 

 from the rest of the heart. In this case it must be regarded 

 as of a different nature from the arrest produced by electrical 

 excitation. 



If it were not for experiment 5, we should be inclined to 

 adopt the former of these views : for it is very easy to imagine 

 that it is not likely to make much difference whether we 

 squeeze the ganglion with a ligature, nip it between the blades 

 of a pair of scissors, or excite it by Faradaic electricity. In- 

 deed, any one who compares the two results the arrest of 

 the heart by electrical excitation of the sinus on the one hand, 

 and that produced by ligature across the upper part of the 

 auricles on the other would probably at once decide on their 

 identity. By previously subjecting the heart to the influence 

 of atropin, we are enabled to demonstrate that such a conclu- 

 sion would be erroneous ; for if the effect of ligature were of 

 the same nature, it would be counteracted by the same agenc3 r . 



In order to explain the phenomena, it is necessary to assume, 

 what has not yet been proved anatomically, namely, that the 

 venous sinus contains an automatic motor centre. By this 

 term we understand (in accordance with the general notions 

 entertained as to rythmical action) aganglionic centre, in which 

 energy tends to accumulate and discharge itself in the form 

 of motion at regular intervals, the length of which varies (a) 

 with the resistance to the discharge, and (6) with the rapidity 

 of accumulation. 



The physiological ground for this assumption of the exist- 

 ence of a motor centre in the sinus venosus is, first, that the 

 succession of acts which make up a cardiac contraction com- 

 mences distinctly in the sinus, and that it is the only part of 

 the heart which contracts independently, i.e., without being 

 affected by the action of any other part of the organ ; and, 

 secondly, that electrical stimulation of the sinus induces in- 

 creased frequency of the contractions of the whole organ. Ad- 

 mitting the existence of such a centre, and assuming also that 

 the ganglion of the vagus, situated, as we have seen it to be, 

 close to the line of ligature or amputation on the auricular 

 side of it, has the power of inhibiting, i.e., increasing the re- 

 sistance to the discharges from that centre, and further that 

 it exercises a similar inhibitory influence on the motor ganglia 

 at the base of the ventricle, we are enabled to harmonize the 

 experimental results completely thus: In the ligature and am- 



