RHYTHM OF THE HEART. 139 



system, have failed to prove that the action is directly 

 governed by the power of any portion of the brain or 

 spinal cord. The results of the experiments are, in many 

 instances contradictory ; but they lead to the general 

 conclusion, that no* uniform and decided alteration in the 

 movements of the heart is produced by irritation of any 

 part of either of those nervous centres. Sudden destruc- 

 tion of either the brain or spinal cord alone, or of both 

 together, produces, immediately, a temporary interruption 

 or cessation of the heart's action : but this appears to be 

 only an effect of the shock of so severe an injury ; for, in 

 some such cases, the movements of the heart are subse- 

 quently resumed, and if artificial respiration be kept up, 

 may continue for a considerable time ; and may then again 

 be arrested by a violent shock applied through an injury 

 of the stomach. While, therefore, we must admit an 

 indirect or occasional influence exercised by, or through, 

 the brain and spinal cord upon the movements of the heart, 

 and may believe this influence to be the greater the more 

 highly the several organs are developed, yet it is clear that 

 we cannot ascribe the regular determination and direction 

 of the movements to these nervous centres. 



The persistence of the movements of the heart in their 

 regular rhythmic order, after its removal from the body, 

 and their capability of being then re-excited by an ordinary 

 stimulus after they have ceased, prove that the cause of 

 these movements must be resident within the heart itself. 

 And it seems probable, from the experiments and observa- 

 tions of various observers, that it may be connected with the 

 existence of numerous minute ganglia of the sympathetic 

 nervous system, which, with connecting nerve-fibres', are 

 distributed through the substance of the heart. These 

 ganglia appear to act as so many centres or organs for the 

 production of motor impulses ; while the connecting nerve- 

 fibres unite them into one system, and enable them to act 

 in concert and direct their impulses so as to excite in 



