112 THE CIRCULATION. 



brain and spinal cord upon the action of the heart, proves that 

 it is not altogether, or at all times, independent of the cerebro- 

 spinal nervous system. Yet the numerous experiments insti- 

 tuted for the purpose of determining the exact relation in 

 which the heart stands towards this system, have failed to prove 

 that the action is directly governed under ordinaiy circum- 

 stances by the power of any portion of the brain or spinal cord. 

 Sudden destruction of either the brain or spinal cord alone, or 

 of both together, produces, immediately, a temporary interrup- 

 tion 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 subsequently re- 

 sumed, 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 in- 

 fluence exercised by, or through, the brain and spinal cord 

 upon the movements of the heart, and may believe this in- 

 fluence to be the greater the more highly the several organs 

 are developed, yet it is clear that we cannot ascribe the regu- 

 lar determination and direction of the movements to these 

 nervous centres. 



The persistence of the movements of the heart in their regu- 

 lar 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 move- 

 ments must be resident within the heart itself. And it seems 

 probable, from the experiments and observations of various 

 observers, that it is 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 con- 

 necting nerve-fibres unite them into one system, and enable 

 them to act in concert and direct their impulses so as to excite 

 in regular series the successive contractions of the several 

 muscles of the heart. The mode in which ganglia thus act as 

 centres and co-ordinators of nervous power will be described in 

 the chapter on the NERVOUS SYSTEM ; and it will appear prob- 

 able that the chief peculiarity of the heart, in this respect, is 

 due to the number of its ganglia, and the apparently equal 

 power which they all exercise ; so that there is no one part of 

 the heart whose action, more than another's, determines the 

 actions of the rest. Thus, if the heart of a reptile be bisected, 

 the rhythmic, successive actions of auricle and ventricle will 

 go on in both halves : we therefore cannot say that the action 



