310 EXPEllI MENTAL INVESTIGATION OF THE ACTION OF MEDTCINESL 



between the two auricles. The reason of this supposition 

 is that, when the venous sinus is separated from the rest of 

 the lieart, it continues to pulsate ; but the auricles and ven- 

 tricles stand still. When the ventricle is cut off from the 

 auricles, it begins to beat again, but the auricles do not ; so that 

 it would seem as it the motor apparatus in the venous sinus and 

 ventricles together could overcome the inhibitory apparatus in 

 the auricles, and keep the heart going ; but that this is too 

 strong- for the motor ganglia in the ventricle alone, and will not 

 let tliem go on till they are separated from it, or till it becomes 

 exhausted, which it seems to do after a little, and then both 

 auricles and ventricles begin anew. The physiologists who 

 hold the simpler view, say that this stoppage is only due to the 

 irritation of the vagus-fibres which run along the venous sinus, 

 and that the renewed cardiac contractions are simply due to 

 the irritation passing off. The pharmacologist, however, is not 

 contented even with the more complicated of these mechanisms, 

 but demands a still more elaborate nervous apparatus in order to 

 explain the action of poisons on the heart. The necessity for this 

 has been clearly shown and a plan of the nerves drawn up by 

 Professor Schmiedeberg. I have endeavoured to represent the 

 supposed nature of this apparatus in the accompanying diagram. 

 (Fig. 138.) It consists of a ganglion m, which keeps up a rhyth- 

 mical contraction of those muscular fibres of the heart to which 

 it is connected by the fine nervous filaments E. This ganglion 

 is connected by an intermediate apparatus, B, with an inhibitory 

 ganglion I, which can retard or stop the muscular contractions 

 which M produces ; and by another apparatus c, w^ith another 

 gauglion Q, which quickens the contractions. I is connected by 

 an intermediate apparatus. A, with the retarding fibres v, of the 

 vagus, and Q by a' with the quickening nerves s, of the heart. 



Inhibitory Ganglia of Heart. — We have hitherto included 

 under the terms vagus-ends ' all the inhibitory apparatus in 

 the heart ; but, when we begin to experiment with the heart 

 alone, we find that poisons which such experiments as have 

 already been described would lead us to class together as acting 

 on the vagus ends, really act on very different parts of the 

 cardiac nervous system. Thus nicotia, when injected into the 



