Schiff' also found that when the heart's action has been made to cease by application of the wires to the groove between the au ricles and ventricles, this effect cannot be counteracted by applying them to the bulbus arteriosus. The phenomenon of the cessa tion of the heart's action, produced by the application of the galvanic stimulus to the pneumogastric, he explains by supposing that its fibres are in a state of activity during the systole of the corresponding part of the heart, but quickly become ex . hausted, thus allowing the diastole to take place: thereafter, their activity being again renes‘ed, a second systole results. When therefore, strong galvanic stimuli are applied to the nerve the state of exhaustion continues longer and in the same proportion the dia stole, or cessation of the heart's action, is also longer.
In accordance with the above views, Valen tin * in like manner holds that the sympa thetic has no influence over the movements of the heart in the frog, neither giving rise to acceleration nor stoppage of its action.
In regard to the connection between the central masses of the nervous system and the action of the heart, it is evident, from what has been above stated in regard to the effects which are produced by the application of the galvanic stimulus to the pneumogastric nerve, that a certain influence must he exercised by these. By Willis f, and others, it was held t'nat the movements of the heart, as well as of the other inorganic muscles, depend upon the cerebellum. This they believed from the circumstance that the nerves which preside over the involuntary actions were supposed to take their origin from this part of the ner vous system, and also from observing that wounds upon the back part of the head proved speedily fatal. HallerI, again, endeavoured to show that the action of the heart is en tirely independent of nervous influence, and is due merely to the inherent irritability of the muscular fibres. From the circumstance that sudden destruction of the spinal cord im mediately produces an interruption of the heart's action, Legallois concluded that its movements are not due to inherent irritability, as Haller maintained, but depend upon the spinal cord. The cessation produced in the way just stated, although indicating that an influence may be exercised through the cen tral nervous masses upon the movements of the heart, by no means implies the conclusion which was drawn frorn it by Legallois, in asmuch as the heart may sometimes in such cases again begin to pulsate. That the heart may be influenced in its action through the medium of the central masses of the nervous system is also shown by the effects which are produced by the application of the galvanic stimulus to these parts. Thus, in the frog, as shown by the experiments of Weber *, Budgef, Valentin 1, and others, it may be made to cease pulsating by applying the wires of the niagneto-electric rotation apparatus to either side of the medulla oblongata. Unless there has been much loss of blood in exposing the parts the heart becomes dark-red, and is very much distended ; where the large blood vessels have been previously cut the heart still ceases to pulsate when the stimulus is applied as above: it does not, however, pre sent the dark-red distended appearance, but is more or less collapsed and pale. The ex periment, according to them, seldom or never fails. If the electric stimulus has been ap plied for too long a time the heart again begins to beat, in the same way as takes place %hen the stimulus is applied to the trunk of the pneumogastric nerve. The same stimulus also
sometimes produces more or less change in the rhythm of the organ. According to the Webers, the portion of the central nervous masses which, when stimulated in this man ner, gives rise to a cessation in the action of the heart, is that extending from the corpora quadrigemina to the posterior extremity of the calamus scriptorius. Budge found, in his experiments, that the corpora quadrigernina were not so intimately concerned in the pro duction of these effects as the medulla ob longata. Tiedemann § appears to regard the cerebellum and the medulla oblong,ata as the parts through which the cessation of the heart's action may be induced, while stimulus applied to the corpora quadrigemina produces no effect. Valentin believes that while the corpora quadrigemina and cerebellum exercise a certain influence, the medulla oblongata is the part chiefly concerned. In nine mice, which were rendered insensible by chloroform, and whose hearts and medulla oblongata were laid bare, Valentin endeavoured to ascertain the parts of the central nervous masses which, when stimulated in the way above mentioned, give rise to cessation of the heart's action, as also the effects which are produced by the same stimulus lalien applied to the spinal cord. In none of them did he observe any stoppage of the heart's action when the cere bellum, or corpora quadrigemina were the parts to which the stimulus was applied : when applied to the medulla oblongata, on the other hand, this effect was invariably pro duced. The cervical part of the spinal cord, when stimulated, gave different results. In a mouse, which had been under the influence of the narcotic for 2,4. minutes, the heart was repeatedly rnade to cease pulsating when the wires were applied upon either side of the spinal cord in the region of the third to the fourth cervical vertebra, and also when ap plied to the part between the first and second cervical vertebrx. After repeating this ex periment several times, and with the same result, he cut the spinal cord across in the region of the second to the third vertebra ; w hen the stimulus was now applied to the loNs er cut extremity of the cord the heart's action was accelerated. The cessation produced by application of the stimulus to this part of the spinal cord in the former experiment was, therefore, according to Valentin, probably due to its being transferred along the spinal cord to the medulla oblongata. In two other animals it was found that the two lower thirds of the cervical portion of the cord in like manner gave rise to no cessation in the heart's action, but rather, after the first few seconds, caused it to he accelerated. A young rabbit was strangled, the head se parated from the body at the articulation between the occipital and first cervical ver tebrm, and artificial respiration kept up. When the wires of the battery, moderately loaded, were now applied to the upper part of the spinal cord, in the reg,ion of the first cervical vertebra, the heart, which was before at rest, commenced pulsating. The spinal cord was laid bare from the first cervical to the eighth thoracic vertebra. When the wires were inserted in the region of the fifth cer vical to the second thoracic vertebra, the heart's action was distinctly accelerated. When the spinal cord was removed, the same result still followed upon application of the wires, because the roots of' the nerves were stimulated. When the heart was cut out of the body, and again placed in situ, the above experiment was repeated without effect.