86 INTRA-CARDIAC GANGLIA. 



increased arterial pressure by excitation of the cervical 

 part of the spinal cord, is attributable to direct excita- 

 tion of the accelerator fibres it contains. Accelerator 

 nerves, i.e., nerves of which the excitation induces increased 

 frequency of action without in any other way affecting 

 the circulation, reach the heart from the spinal cord 

 through the sympathetic system. In the rabbit, they ap- 

 proach the heart through the inferior cervical ganglion ; in 

 the dog they are derived chiefly from the dorsal ganglia, 

 from the 1st to the 5th. In all cases there is a delay 

 of several seconds between the excitation and the effect. 

 When the inhibitory and accelerator nerves of the heart 

 are excited simultaneously, the effects balance each 

 other. 



Infra-cardiac Ganglia and Nerves of the Heart. The 

 nervous system of the heart of the frog consists of (i) a 

 plexus, which is situated in the septum between the 

 auricles, close to the opening by which the right auricle 

 communicates with the sinus venosus. This is con- 

 nected by nerve filaments with (2) smaller groups of 

 ganglion cells (Bidder's ganglia) in the neighbourhood of 

 the auriculo-ventricular furrow. Collections of ganglion 

 cells exist in other parts of the heart, but their arrange- 

 ment is imperfectly known. The phenomena relating to 

 the functions of the intra-cardiac ganglia may be studied 

 in the heart after its removal from the body, either in the 

 empty state or when supplied with blood or other nutrient 

 liquid in such a way as to enable it to fill and discharge 

 itself under natural conditions. The liquid used must 

 contain the salts of the blood, and a trace of proteid, but 

 need not contain haemoglobin. Mechanical or electrical 

 excitation of the dorsal surface of the right auricle 

 (inhibitory centre) arrests the heart in diastole. Accord- 

 ingly, if a tight ligature is placed round the heart in 

 this position, it loses the power of rhythmical contrac- 

 tion. If, thereupon, the auricles are cut off from the 



