AUTHOR'S DIAGRAM OF CARDIAC GANGLIA. 311 



blood after the vagi and cord have been divided, renders the 

 pulse slow ; but this soon gives way to quickening ; or, if the 

 dose be large, quickening may occur at once ; and, if we then 

 irritate the vagus, we find that we cannot render the heart 

 beats slow any more than we can after poisoning by atropia. 

 We thus see that, after the irritation which nicotia first occa- 

 sions in the vagus- ends has passed off, it paralyses them ; and 

 we might thus be inclined to think that they acted on the same 

 structures. But, if we give nicotia to a frog, and instead of 



Fig. 138. — Diagram of the hypothetical Nervous Apparatus in the Heart. 



M, motor ganglion, i, inhibitory ganglion. Q, quickening ganglia, v, inhi- 

 bitory fibres ; and S, quickening fibres from the medulla. A, a'', b and C, inter- 

 mediate apparatus, e, fibres passing from the motor ganglia e, to the muscular 

 substance f. For simplicity's sake, only one set of motor ganglia has been 

 represented, but other similar ones are to be supposed to be present in other 

 parts of the heart, and so connected with this set that they all work in unison. 

 It must be remembered that this diagram is purely hypothetical ; but if this be 

 carefully borne in mind, the sketch will be found of service in remembering and 

 comparing the action of difierent poisons on the heart. 



irritating the vagus, we irritate the venous sinus, still-stand of 

 the heart is at once produced ; while, if atropia be given, and 

 the venous sinus then be irritated, the pulsations are nob slowed 

 at all — showing us that there is some inhibitory apparatus in the 

 venous sinus which has been paralysed by atropia, but left 

 untouched by nicotia. We may substantiate this conclusion by 

 another and extremely useful method of investigation — viz., by 

 administering another poison, and seeing how its action is 

 affected by each of the other two. If we allow a Httle muscaria 



