INFLUENCE OF THE NERVOUS SYSTEM. 169 



quantity of blood. So, at the moment of death, the pulse 

 may be very rapid, while the circulation declines. 



The heart, when taken from the body, may still continue 

 to beat : this may be readily observed in the cold-blooded 

 animals, and has also been found to be the case in man ; we 

 have found rhythmical contractions still existing in the heart 

 of an executed criminal an hour after death. This is, how- 

 ever, only another reflex phenomenon, the centre for which is 

 found in small ganglions disseminated throughout the sub- 

 stance of the coats of the heart, principally in the auricles 

 and the auriculo-vejitricular zones, or, at all events, near the 

 base of the heart. If the heart of a frog be cut in fragments, 

 we find that only those parts of the ventricle or of the auri- 

 cles which adhere to the base continue to palpitate. 



The position of these ganglions, or small reflex centres, 

 found in the heart itself, has been ascertained up to a certain 

 point: there are three principal ones, ganglion of Remak, 

 at the opening of the lower vena cava; ganglion of Bidder, 

 situated in the left auriculo-ventricular septum ; and gan- 

 glion of Ludwig, in the inter-auricular septum. 



These three ganglions do not all appear to have the same 

 function : the two former appear to be centres of excita- 

 tion, and the latter of moderation. If the heart be cut into 

 two unequal parts, one containing Remak's ganglion, and 

 the other those of Bidder and Ludwig, the first will continue 

 to palpitate, while the other remains quiet. If then the auri- 

 cles in this latter part be separated from the ventricle, they 

 will remain in repose, while the ventricle again begins to 

 throb. Thus we see that each of the outer ganglions 

 (Remak's and Bidder's) cause movements which the inner 

 ganglion (Ludwig's) paralyzes, when taken in connection 

 with only one of the two first; but when the heart is entire, 

 Jjiid wig's ganglion is unable to counterbalance the amount 

 of motor-power of the other two. 



The starting-point for these reflex actions is the excitation 

 produced by the presence of the blood on the sensory (or 

 centripetal) fibres in the endocardium, and not directly on 

 the muscular fibre itself. A substitute for this physiological 

 excitant may be found, in experiments, by excitations di- 

 rected to any point of the heart, particularly the endocar- 

 dium. If the contact of the blood with the endocardium be 

 prevented the heart ceases its pulsations, the physiological 

 cause of the reflex action being thus removed. If, for in- 

 stance, the chest, and consequently, the heart, be forcibly 



