ACTION OF THE HEART. 547 



had absolutely become so dry, as to rustle during its movements. It has 

 lately been shown by Mr. Todd, that the irritability of the heart is of long 

 duration after death in very young animals : which, as long since demonstrated 

 by Dr. Edwards, agree with the cold-blooded Vertebrata in their power of 

 sustaining life, for a lengthened period, without oxygen. It is difficult to ac- 

 count for the long continuance of the alternate contractions and relaxations of 

 the muscular parietcs of the heart, after all evident stimuli have ceased to act 

 upon it; and many theories have been offered on the subject, none of which 

 afford an adequate explanation. The extraordinary tendency to rhythmical 

 action, which distinguishes the heart from all other muscles, is shown by the 

 fact that not only do the entire hearts of cold-blooded animals continue to act, 

 long after their removal from the body, but even separated portions of them 

 will contract and relax with great regularity for a long time. Thus the auri- 

 cles will persist in their rhythmical action, when cut off above the auriculo- 

 veritricular rings ; and the apex of the heart will do the same, when separated 

 from the rest of the ventricle. The stimulus of the contact of blood with the 

 lining membrane of .the heart, to which its regular actions have been com- 

 monly referred, can have no influence in producing these movements; nor 

 does it appear that the contact of air can take its place ; since, as Dr. J. Reid 

 has shown, the rhythmical contractions of the heart of a frog will continue 

 in vacua. Nor is there any evidence that the flow of blood through the 

 cavities has the effect of securing the regularity of their successive contrac- 

 tions in the living body ; for this regularity is equally marked in the contrac- 

 tions of the excised heart, when perfectly emptied of blood, so long as its 

 movements continue vigorous. But when its irritability is nearly exhausted, 

 the usual rhythm is often a good deal disturbed, so that the contractions of 

 the auricles and ventricles do not regularly alternate with each other ; and one 

 set frequently ceases before the other. 



a. It was formerly supposed, that the movements of the Heart were dependent upon its 

 connection with the centres of the Cerebro-Spinal nervous system ; and the experiments of 

 Legallois and others, who found that they were arrested by crushing, or otherwise suddenly 

 destroying, large portions of these centres, appeared to favour the supposition. But it has 

 been shown by Dr. Wilson Philip and his successors in the same inquiry, that the whole 

 Cerebro-Spinal axis might be gradually removed, without any such consequence; which 

 fact harmonizes perfectly with the "experiments prepared for us by Nature," in the pro- 

 duction of monsters destitute of these centres, which nevertheless possessed a regularly- 

 pulsating heart. As already mentioned ( 416), it is difficult to obtain any distinct evidence, 

 that the actions of the heart are affected by any ordinary irritation of the Par Vagum ; but 

 the recent experiments of MM. Weber have shown that its movements may be immediately 

 arrested, by the transmission of the electric current from a rotating magnet, either through 

 the Spinal Cord, or through the Vagi nerves divided at their origin. The same irritation, 

 however, applied to a single one of the Vagi, produced no effect.* 



b. It has latterly been the fashion with many, however, to attribute the action of the Heart 

 to the Sympathetic system ; but of this there is no sufficient evidence. The possibility of 

 exciting the action of the heart through the Sympathetic nerve ( 576), shows that this may 

 have an influence on its movements; whilst the great difficulty with which any evidence 

 to this effect can be procured, seems a sufficient proof, as in the case of the Muscular coat of 

 the intestines ( 388), that this influence cannot be nearly adequate to the constant main- 

 tenance of a function so energetic. Some have more recently maintained, that the move- 

 ments are of a strictly reflex nature, and that fliey are effected through the agency of certain 

 minute ganglia, belonging to the Sympathetic system, and scattered through the substance of 

 the heart ; in this way endeavouring to account for the persistence of the motions of the 

 organ after its complete removal from the body, and under circumstances which suspend all 

 reflex movements that have their centre in the cerebro-spinal system. But this attempt at 

 explanation affords no aid in the solution of the cause of the continued rhythmical move- 

 ments of the organ, or of its separated portions, after the withdrawal of all stimuli that can 

 be supposed to operate in exciting them ; and the phenomena are just as fully explained by 



* Archives d'Anat. Gener. et de Physiol., Janv. 1846. 



