1 06 THE INVOL UNTAR Y NER VO US S YSTEM 



removal of the nerve-cell the condition of the muscle is pro- 

 foundly altered ; and it is, in my opinion, highly probable that the 

 normal beat of the heart is dependent on the muscular tissue, 

 where the beat originates, being kept in the due condition for 

 spontaneous contractions by the action of nerve cells in the 

 heart. The whole object of my researches on the rhythm of the 

 heart was to answer the two questions : " Do motor nerve cells 

 in the heart send out rhythmic impulses to the muscular struc- 

 tures of the heart ? " and " Is the sequence of the contractions of 

 the different heart cavities due to impulses passing along the 

 main intra-cardiac nerves, which reach the muscular structures of 

 the separate cavities in orderly sequence ? " These two questions 

 I claim to have answered definitely in the negative. 



The observations of Carlson on the rhythm of the heart of 

 Limulus have served to resuscitate the neurogenic theory of 

 the heart's action. In this animal the cardiac nerve cells are 

 grouped together into a cord, which lies on the surface of the 

 heart and can be easily removed without damaging the muscu- 

 lar tissue in any way. It is found that after removal of this 

 nerve cord the heart entirely ceases to beat. Carlson, therefore, 

 argues that the rhythm of the heart is entirely dependent on the 

 presence of the nerve cells in this cord and is in no way a func- 

 tion of the muscular tissue. He implies that motor nerve cells 

 in the cord discharge rhythmic impulses along the nerves in 

 the heart, and that the heart muscle contracts to each impulse ; 

 in fact, that the motor nerves to the heart muscle resemble the 

 phrenic nerves to the diaphragm in the part played by them in 

 the rhythmic contraction of the muscle. Carlson has not, how- 

 ever, yet completed the resemblance, for he has not been able to 

 show by means of the galvanometer that rhythmic discharges 

 do pass along these cardiac nerves when the heart is beating, as 

 can be shown in the phrenic nerve in the case of the respiratory 

 discharges. Further, and this seems to me a very important con- 

 sideration, Carlson states that the removal of the nerve cord 

 leaves the muscular tissue in a condition of inhibition similar to 

 that caused by stimulation of the inhibitory nerves, from which 

 he argues that the inhibitory nerves act by removal of the im- 

 pulses from the motor nerve cells and not by direct action on the 

 muscular tissue ; but it also shows that the condition of the 

 cardiac musculature is profoundly altered by removal of the 



