434 Prof. Huxley^ on the present state of Knowledge [May 15, 



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 excitement 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 de- 

 tailed — 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 conclu- 

 sion. An 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 

 seen 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 

 heart, and whenever these fibres are irritated the rhythmical action 

 ceases. The pneumogastric nerves must act either directly upon 

 the muscles of the heart, or indirectly through the ganglia, into 

 which they can be traced. If the former alternative be adopted, 

 then we must conceive the action of the pneumogastric nerve upon 

 muscle to be the reverse of that of all other nerves — for irritation 

 of every other muscular nerve causes activity and not paralysis of 

 the muscle. Not only is this in the highest degree improbable, but 

 it can be demonstrated to be untrue ; for on irritating, mechanically, 

 the surface of the heart brought to a standstill by irritation of the 

 pneumogastrics, it at once contracts. The paralysing influence 

 therefore is not exerted on the muscles, and as a consequence, we 

 can only suppose that this " negative innervation," as it might be 

 conveniently termed, is the result of the action of the pneumogastric 

 on the ganglia. 



It results from all these experiments, firstly, that nerve substance 

 possesses the power of exciting and co-ordinating muscular actions; 

 and secondly, that one portion of nervous matter is capable of con- 

 trolling the action of another portion. In the case of the heart it 



