BY DR. BURDON-SANDERSON. 287 



have any power of augmenting the energy of the heart's con- 

 tractions, or of causing it to do more work in a given time, 

 there are certain nerves by which the distribution of its efforts 

 in time may be modified in the direction of greater frequency. 

 Bv the following experiment it can be shown that the accele- 

 ration of pulse which is produced bj< electrical excitation of 

 the severed spinal cord is independent of increase of arterial 

 pressure. 



In a curarized rabbit in which respiration is maintained arti- 

 ficially, the spinal cord is severed from the medulla, and the 

 vagi, sympathetics, and depressors are divided. The arterial 

 pressure of course sinks to about an inch of mercury, and the 

 pulse becomes slower. The cord is then excited electrically. 

 The pressure rises at once to four or five inches, the rate of 

 the heart's contractions also increasing, but not in proportion 

 to the rise of pressure. As soon as the effects of stimulation 

 have subsided, and the circulation has had time to resume its 

 former condition, both splanchnics are divided, in consequence 

 of which the pressure again sinks a few millimetres. The key 

 is opened : again we have acceleration of the pulse, but this 

 time, the nerm pressores having been divided, the excitation 

 produces hardly any effect on the arterial tension. The results 

 of one of Ludwig's experiments are as follows: After section 

 of the depressors, vagi, and sympathetics, arterial pressure 60 

 millimetres, pulsations in 15 seconds, 52 ; after section of cord, 

 arterial pressure 20 millimetres, pulsations 45 ; during excita- 

 tion of cord, arterial pressure 80 millimetres, pulsations 61; 

 after section of splanchnics, arterial pressure 10 millimetres, 

 pulsations 27; during excitation of medulla, arterial pressure 

 12 millimetres, pulsations 42. 



81. Proof that the Inferior Cervical Ganglion is 

 the Channel by which the Direct Influence of the 

 Spinal Cord on the Heart is exercised. Before pro- 

 ceeding to describe the experiments by which this is shown, 

 it will be necessary to give an account of the anatomical rela- 

 tions of the lowest cervical ganglion in the rabbit and dog. 

 It is obvious, from what we know of the anatomy of the 

 cardiac nerves as well in man as in the lower animals, that, 

 with the exclusion of the vagus, the only channels by which 

 the spinal cord can influence the heart directly are the rami 

 communicantes, by which it is united with the ganglia. By 

 experiment we learn that the communicating filaments by 

 which the accelerating influence of the cerebro-spinal centres 

 is transmitted, are those which enter the inferior cervical 

 ganglion. 



In the rabbit, the trunk of the cervical sympathetic ends at 

 the root of the neck, in the inferior ganglion. This ganglion 

 lies deepl}- on the surface of the muscles which cover the spinal 



