A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

  • Landois, Leonard
Date:
1888
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Licence: Public Domain Mark

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    as a rule the ventricle begins at once to beat again, whilst the auricles remain in the condition of diastolic rest. [Thus the sinus venosus and ventricle continue to beat, -svhile the auricle stands still, but the two former no longer beat with the same rhythm, the ventricle usually beats more slowly, as is shown in fig. 58, 2, by the large zig-zags.] According to the position of the second ligature or incision, the auricles may also beat along with the ventricles, or the auricles alone may beat, while the ventricles remain at rest. Theoretical.—Various explanations of these experiments have been given :—(a) Remak's ganglion in the sinus venosus is distinguished by its great excitability, while Bidder's ganglion in the auriculo-ventricular groove is less excitable ; in the normal condition of the heart the motor impulse is carried from the former to the latter. If the sinus venosus be separated from the heart, Remak's ganglion has no action on the heart. The heart stops for two reasons— first, because Bidder's ganglion alone has not sufiicient energy to excite it to action, and because the inhibitory fibres of the vagus going to the heart have been stimulated by being divided at this i)oint {Hcidcnhain). [That stimulation of the inhibitory fibres of the vagus is not the cause of the standstill, is proved by the fact that the standstill occurs even after the adminis- tration of atropine, which paralyses tlie cardiac inhibitory mechanism.] The passive heart, however, may be made to contract by mechanically stimulating Bidder's ganglion, e.g., by a slight prick with a needle in the auriculo-ventricular groove, or by the action of a constant current of moderate strength {Eckhard), the ventricular pulsation at the same time preceding the auricular {v. Bczold, Bernstein). If the auriculo-ventricular groove be divided, the ventricle pulsates again, because Bidder's ganglion has been stimulated by the act of dividing it; while, at the same time, the ventricle is withdrawn from the inhibitory influence of the vagus pro- duced by the first division at the sinus venosus. If the line of separation is so made that Bidder's ganglion remains attached to the auricles, these pulsate, and the ventricle rests ; if it be divided into halves, the auricles and ventricles pulsate, each half being excited by the portion of the ganglion in relation with it. {b) According to another view, both Remak's {a) and Bidder's ganglia {b) are motor centres, but in the auricles there is in addition an inhibitory ganglionic system (f) {Bczold, Traube). Under normal circumstances a + b is, stronger than c, while c is stronger than a or & separately. If the sinus venosus be separated it beats in virtue of a ; on the other hand, the heart rests because c is stronger than b. If the section be made at the level of the auriculo-ventricular groove, the auricles stand still owing to c, while the ventricle beats owing to b. (2) If the ventricle of a frog's heart be separated from the rest of the heart by means of a ligature, or by an incision can-ied through it at the level of the auriculo-ventricular groove, the sinus and atria pulsate undisturbed as before {Descartes, 1644), but the ventricle stands still in diastole. A single local stimulus applied to the ventricle is responded to by a single contraction. If the incision be so made that the lower margin of the auricular septum remains attached to the ventricle, the latter pulsates. Even the ventricles of a rabbit's heart, when separated vi^ith a part of the auricles in connection with them, pulsate {Tvjerstedt). [Gaskell's Clamp.—Gaskell uses a clamp, regulated by a millimetre screw, to compress the heart, and thus to obstruct the passage of impulses frora'one part of the heart to the other, or to block the way, the pulsations of the auricles and ventricles being separately registered. By compressing the heart at the auriculo-venti icular groove, the ratio of auricular and ventri- cular beats alters, and instead of being 1 : 1, there may be 2, 3, or more auricular beats for each beat of the ventricle, expressed thus— ^ . ^ , 11? , _ After the heart is fixed by the clamp, levels are placed horizontally above and below the heart. These levers are fixed to part of the auricles and to the a])ex by means of threads. Each part of the heart attached to a lever, as it contracts, pulls upon its own lever, so that the extent and duration of each con- traction may be registered. This method is applicable for studying the etiect of the vao-us and other nerves upon the heart.] ° (3) Section.—A. Fick showed that the process of excitement in the contractile tissue of the frog's heart is propagated in all directions (1874), so that to a certain extent the whole frog's heart behaves like one continuous muscular fibre, thus one transverse cut into the ventricle does not prevent contraction from taking place in the separated parts. Eugelmann's experiments also show that if the ventricle of a frog's heart be cut up into two or more strips in a zig-zag way, so that the individual parts still remain connected with each other by muscular tissue, the
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