72 Royal Institution .— 



the regulative power is seated, uot only in the heart itself, but in 

 definite regions of the organ. Reraoye the heart from the body, 

 and it still goes on beating ; the source of the rhythm is therefore 

 to be sought in itself. If the heart be halved by a longitudinal 

 section, each half goes on beating ; but if it be divided transversely, 

 between the line of junction of the auricles with the ventricle and 

 the apex of the latter, the detached apex pulsates no longer, while 

 the other segment goes on beating as before. If the section be 

 carried transversely through the auricles, both segments go on 

 beating ; and if the heart be cut into three portions by two trans- 

 verse sections, one above the junction of the auricles and ventricle, 

 and one below it, then the basal and middle segments will go on 

 j)ulsating, while the apical segment is still. Clearly then, the source 

 of the rhythmical action, the regulative power, is to be sought some- 

 where about the base of the auricles, and somewhere about the 

 junction of the auricles and ventricles. 



Now there is in the frog's heart, besides the three tissues which 

 have been mentioned, a fourth, the neiTous tissue. A ganglion is 

 placed at the base of the heart, where the great veins enter the 

 auricles — from this two cords can be traced traversing the auricular 

 septum, and entering two other ganglia placed close to the junction 

 of the auricles with the ventricles. From these ganglia nerves are 

 distributed to the muscular substance. Now we know, from evidence 

 afforded by other striped muscles and nerves, that the contraction of 

 the former is the result of the excitement of the latter ; in like 

 manner, we know that the ganglia are centres whence that excite- 

 ment originates. We are therefore justified, analogically, in seeking 

 for the sources of the contractions of the cardiac muscles, in the 

 cardiac ganglia ; and the experiments which have been detailed — by 

 showing that the rhythmical contractions continue in any part of the 

 heart which remains connected with these ganglia, while it ceases in 

 any part cut off from them — prove that they really are the seats of 

 the regulative power. 



The speaker then exhibited another very remarkable experiment 

 (first devised by Weber) which leads indirectly to the same con- 

 clusion. x\n electro-magnetic apparatus was so connected with the 

 frog upon the table, that a series of shocks could be transmitted 

 through the pneumogastric nerves. When this was done, it was 

 geen that the index almost instantly stopped, and remained still, so 

 long as the shocks were continued ; on breaking contact, the heart 

 remained at rest for a little time, then gave a feeble pulsation or 

 two, and then resumed its full action. This experiment could be 

 repeated at will, with invariably the same results ; and it was most 

 important to observe, that during the stoppage of the heart, the 

 index remained at the lowest point of its arc, a circumstance which, 

 taken together with the distended state of the organ, showed that its 

 stoppage was the result, not of tetanic contraction, but of complete 

 relaxation. 



Filaments of the pneumogastric nerve can be traced down to the 

 lieart, and whenever these fibres are irritated, the rhythmical action 



