SYMPATHETIC NERVE. 



463 



lie parallel to one another, as in the ordinary 

 muscles, but cross one another in different di- 

 rections, many of the bundles being at the 

 same time observed to present a more or less 

 branching character. The branches or divi- 

 sions of one bundle cross those of neighbour- 

 ing bundles. In this manner the fibres form 

 a number of reticulated layers laid over one 

 another, while at the same time bundles pass 

 from one layer into the adjacent layers, so 

 that a more or less complete intermixture of 

 the fibres takes place. The fibres composing the 

 ventricles also present more or less of this re- 

 ticulate arrangement. Moreover, many of the 

 fibres of the auricles pass into those of the 

 ventricle, and vice versa. In virtue of such an 

 arrangement of the fibres, stimulus applied to 

 one part of the heart gives rise to a contrac- 

 tion in the bundle to which it is applied : since 

 this crosses neighbouring bundles its con- 

 traction acts as a stimulus to these, in obe- 

 dience to which they also contract. In this 

 manner, the contraction is not limited to the 

 fibre, or bundle of fibres, to which the stimulus 

 is first applied, but extends over the entire 

 mass. So also the contraction of the fibres, 

 which are described as passing bet ween theauri- 

 cles and ventricles, stimulate the fibres of which 

 the latter are composed, giving rise to a ge- 

 neral contraction in them also ; and in this way 

 the successive contraction of auricles and 

 ventricles is produced. According to Schiff, 

 as mentioned by Valentin, the movements 

 of the heart may be reduced to the peri- 

 staltic or vermicular type. He holds that 

 in a certain part of the muscular substance 

 are contained the nerves which preside over 

 the movements of neighbouring bundles. 

 When this contracts, a stimulus is thereby 

 given to the nerves which supply the portion 

 of the muscular substance immediately suc- 

 ceeding ; so that in this manner a number of 

 progressive contractions of the successive 

 bundles of fibres are produced. The contrac- 

 tion of the auricles or ventricles is thus not a 

 single simultaneous act ; but is made up of a 

 great number of contractions succeeding one 

 another, in the same manner as is seen in the 

 contraction of the intestine. It is the rapidity 

 with which they follow one another that gives 

 rise to the appearance of their being simul- 

 taneous. These contractions travel from 

 auricle to ventricle, giving rise to the successive 

 contractions of these parts. He finds that 

 when a ring of the muscular substance at the 

 base of the ventricle in the frog's heart is 

 brought, by local application of the galvanic 

 stimulus, into a state of continued or spas- 

 modic contraction, the due rhythm between 

 the contraction of the auricles and the part 

 of the ventricle below the contracted portion 

 ceases. When a spasmodic contraction is 

 produced in a part of the ventricle by ex- 

 ternal stimulus this part may be irritated 

 without giving rise to any general contraction. 

 He also finds that when a portion of the 

 ventricle of a heart which still retains its ir- 

 ritability, is stimulated, the contraction is 

 sometimes seen to take place in this before it 



takes place in the other portions ; the stimu- 

 lated portion is also the part which first be- 

 comes relaxed in the diastole of the organ. 



In opposition to the view above mentioned 

 Volkmann* maintains that the movements of 

 the heart cannot depend upon the central 

 nervous masses. It continues its pulsations 

 after the brain and spinal cord have been 

 removed. When, however, the rhythmical 

 movements of a part depend upon a nervous 

 centre, they cease immediately after the con- 

 nection between these parts and the nervous 

 centre is broken. The rhythmical movements 

 of the muscles of respiration depend upon a 

 nervous centre, the medulla oblongata. So 

 soon as this is destroyed they cease. In like 

 manner the heart, were the medulla oblongata, 

 or any other part of the central masses of 

 the nervous system the centre upon which its 

 movements depend, must also cease pulsating 

 so soon as it is removed from the influence of 

 these. According to the experiments of 

 Bidder, however, already mentioned, frogs 

 may live for six weeks after the spinal cord 

 has been destroyed, the circulation, as seen 

 in the web of the foot, going on as livelily as 

 before, and presenting no difference when 

 compared with that in the healthy animal. 

 So also when the entire central masses of the 

 nervous system are removed the heart still 

 continues its pulsations until the second day. 

 The movements exhibited by the heart, after 

 the central masses of the nervous system 

 have been destroyed, cannot, according to 

 Volkmann, be explained as mere movements 

 of irritation, due to the inherent irritability 

 of the muscular fibres, acted on by the 

 stimulus of the blood or of the atmospheric 

 air. Mere irritability, acted on by the stimulus 

 of the blood, or of the air, cannot explain 

 why both auricles or both ventricles should 

 contract at one and the same time ; and just 

 as little can we in this way explain the suc- 

 cessive contraction of auricles and ventricles. 

 To explain the rhythmical order in which these 

 contractions take place it is necessary to sup- 

 pose that they, like movements of a similar 

 kind, such as those of the respiratory muscles, 

 are regulated by a nervous centre. The fact 

 that the heart's movements continue after it 

 has been removed from the body indicates, 

 moreover, that the centre upon which its 

 movements depend must be contained in the 

 organ itself. It has been already mentioned 

 that in different parts of the heart are found 

 small ganglia. These are believed by Volk- 

 mann to be the centres on which its move- 

 ments depend. These, according to him, act 

 as organs from which the impulse to contrac- 

 tion proceeds : they are also so connected 

 with one another as to act in concert, the 

 impulses proceeding in such directions as to 

 give rise to the regular succession in which 

 the contractions of the different parts take 

 place. 



The effects produced upon the heart's 

 action by stimuli applied to the central masses 

 of the nervous system, and upon which the 

 * Loc, cit. p. G16. &c. 



