ACTION OF THE HEART. 471 



excited, save by the successive recurrence of stimuli at regular intervals, as in 

 the act of Respiration. It is the continuance of activity after all conceivable 

 sources of stimulation have been withdrawn, which constitutes the real perplexity 

 of the case; and if the operation of such stimuli be admitted as the sources of 

 reflex action, they may with equal propriety be regarded as directly acting upon 

 the contractile fibre which, as already shown, is much more amenable to such 

 direct excitation, than it is to nervous influence, and preserves its capacity for 

 being impressed by the former during a much longer period than it remains 

 capable of responding to the latter. 



498. A more satisfactory mode of accounting for the rhythmical movements 

 of the Heart, appears to the Author to lie in regarding them as an expression 

 of the peculiar vital endowments of its Muscular tissue ; and to believe that, so 

 long as this tissue retains its integrity, and the other necessary conditions are 

 supplied, so long is an alternation of contraction and relaxation the characteristic 

 and constant manifestation of its vital activity just as ciliary movement is in 

 cells of one class, and secreting action in those of another ( 110). The fact 

 that this movement is seen to commence in the embryo-heart, when as yet its 

 parietes consist of ordinary- eel Is, and no nervous structure exists either in its 

 own substance or in the body at large, is an important confirmation of this doc- 

 trine ; whilst the same fact stands in complete opposition, to the idea, that ner- 

 vous force is in any way concerned in maintaining this rhythmical action. But 

 it may be said that in attributing to the muscular structure of the heart a self- 

 moving power, we really only throw back the question into the obscurity from 

 which the Physiologist has sought to draw it. 1 Such is far from being the case, 

 however, if it can be shown that this self-moving power is nothing else than an 

 exertion of ordinary Muscular Contractility under peculiar conditions; and if 

 analogous phenomena can be shown to present themselves elsewhere. 2 To this 

 point attention will now be directed. 



499. We have seen that the contraction of any Muscle, upon the application 

 of a stimulus, must be attributed to an exercise of Vital Force engendered by 

 previous acts of Nutrition. The stimulus is not the source of the force, but only 

 supplies some condition which is requisite for its manifestation; just as the fall 

 of a spark upon gunpowder causes its explosion (the force of which is the expres- 

 sion of the change in the chemical condition of its components, which change is 

 dependent upon their pre-existing affinities), or as the application of the discharger 

 to the Leyden jar (which has been charged by the previous action of the Elec- 

 trical machine) liberates, so to speak, its pent-up electricity, and allows this to 

 display itself as an active force. Now just as the Leyden jar may be so charged 

 with electricity as to discharge itself spontaneously, so is it easy to conceive that 

 a Muscle may be so charged with motility (or motor force) as to execute sponta- 

 neous contractions; and of the existence of such a condition, we have valid 

 evidence. For there are many local phenomena of cramp and spasm, which 

 cannot be fairly attributed to a perverted reflex action of the nervous system, 

 and which can scarcely be referred to anything else than an overcharge of mus- 

 cular power. So, again, the action of the uterus, as shown not merely in the 



1 In so far as it attributes the Heart's action to causes originating in itself, this doctrine 

 may be considered as nothing else than the old notion of the inherent "pulsific virtue" of 

 the organ, so happily ridiculed by Moliere and Swift. But there is really just the same dif- 

 ference between the two, as between the doctrine of Vital Forces, which it has been the 

 Author's object to unfold in this and the companion Treatise, and the old notion of the 

 "vital principle" which was held to account for everything not otherwise explicable. 



2 It cannot be too constantly borne in mind, in this and other instances, to explain a phe- 

 nomenon in Physiology or in any other science whatever, is nothing else than to show that 

 it is conformable to some general law, and that it is thus a result of some previously recog- 

 nized cause, which is common to it with a number of other previously observed phenomena. 

 (See Mr. John S. Mill's "System of Logic," book iii. chap, xii.) 



