479 



In like manner, it may be that the rhythmic movements of the 

 lymphatic hearts in Amphibia depend on a part of the spinal cord as 

 their nervous centre ; but this is doubtful * ; doubtful I mean, not 

 whether there be a nervous centre for the rhythmic movements, but 

 where it is seated. The case of the respiratory movements, however, 

 is clear, and should be reckoned as of great weight in the argument 

 for the nervous origin of the heart's action. 



The experiments on the heart's action which I have shown, 

 have been selected as the simplest and most significant. I pass by 

 many more, and say concerning them only this, that I believe there 

 are none whose results are inconsistent with the belief that I have 

 expressed as to the cause of the rhythmic action of the heart. There 

 are some, of which the results are difficult to explain ; but the diffi- 

 culties relate to questions of nerve-physiology "f, and do not affect the 

 simple conclusion that the rhythmic action of the heart in theVerte- 

 brata depends on the operation of nervous centres in the ganglia on 

 or near the substance of the heart : I say, in the Vertebrata ; for as 

 yet we know (I believe) nothing of the origin of the corresponding 

 movements in the Invertebrata, though we may well believe that in 

 them, and especially in the lower among them, the rhythmic move- 

 ments of any pulsating vessel, analogous to a heart, are independent 

 of any nervous system. Such a difference in the two great groups 

 would correspond with similar differences in nearly all other parts of 

 their several economies. The more highly developed the nervous 

 system is, the more are its operations influential in those of every 

 other part and system ; and, for the heart, we may suppose that the 

 making-over of its rules of action to a proper nervous system is on 

 purpose that it may the more quickly correspond and sympathize 



* See the Experiments of Schiff, Mayer and Budge, in Canstatt for 1850, 

 p. 126 ; and those of Heidenhain in the same, for 1855, p. 130. 



t I refer, especially, to those on the pneumogastric nerves, of which the con- 

 tinued galvanic stimulus stops the heart's action. The phenomena observed in 

 this and similar experiments appear to me very similar to those of shocks. As 

 a violent shock of any kind may exhaust the power, or suspend the action, of the 

 brain or spinal cord, so may a shock by violence or galvanic force similarly affect 

 the power of the rhythmic nervous centres for the heart. And the general 

 explanation of all may be, that the nutrition of a nervous centre, and thereby the 

 maintenance of its power, requires rest, and that this rest cannot exist while nerves 

 in relation with it are under irritation. 



