Volume 1

A text-book of human physiology : including histology and microscopical anatomy : with special reference to the requirements of practical medicine / by L. Landois ; translated from the seventh German edition, with additions, by William Stirling.

Date:: 1891

Credit: A text-book of human physiology : including histology and microscopical anatomy : with special reference to the requirements of practical medicine / by L. Landois ; translated from the seventh German edition, with additions, by William Stirling. Source: Wellcome Collection.

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

139/602 page 99

$Special Actions of Cardiac Poisons.—The complicated actions of various poisons upon the heart have led observers to suppose that there are various intra-cardiac mechanisms on which these substances may act. Besides the muscular fibres of the heart and its automatic ganglia, -some toxicologists a.ssume that there are inhibitory ganglia into which the inhibitory fibres of the vagus pass, and accelerator ganglia, which ’are connected with the accelerating nerve-fibres of the heart. Both the inhibitory and accelerator ganglia are connected with the automatic ganglia by conducting channels. Muscarin and all other trimethylammonium bases stimulate permanently the inhibitory ganglia, so that the heart stands still {Schmiedeberg a'nd Koppe). According to Ga.slcell, how- ever, when the action of the sinus is arrested by muscarin, there is no deflection of the galvano- meter similar to that produced by the excitation of the vagus. He infers that muscarin does not cause arrest of the beat by acting as an excitant of inhibitory mechanisms, but as a depressant to motor activity.] As atropin and daturin paralyse these ganglia, the standstill of the heart brought about by muscarin may be set aside by atropin. [If a frog’s heart be excised and placed in a watch-glass, and a few drops of a very dilute solution of muscarin be placed on it with a pipette, it ceases to beat within a few minutes, and will not beat again. If, however, the muscarin be removed, and a solution of atropin applied to the heart, it will resume its con- tractions after a short time.] Physostigmin or Calabar bean excites the energy of the cardiac muscle to such an extent that stimulation of the vagus no longer causes the heart to stand still. lodine-aldehyd, chloroform, and chloral-hydrate paralyse the automatic ganglia. The heart stands still, and it cannot be made to contract again by atropin. The cardiac muscle itself remains excitable after the action of muscarin and iodine-aldehyd, so that if it be stimulated it contracts. [According to Gaskell, antiarin and digitalin solutions produce an alteration in the condition of the muscular tissue of the apex of the heart of the same nature as that pro- duced by the action of awery dilute alkali solution, while the action of a blood-solution contain- ing muscarin closely resembles that of a dilute acid solution (p. 110, § 65).] [Some Cardiac Poisons—The cardiac muscle is stimulated, i.e., its contractions become more energetic, the rate of heart-beat remaining the same or becoming slower—under the influence of veratria, digitalin, strophanthus, antiarin, &c., while it is depressed—as shown by diminished energy of contraction, and with final stoppage in diastole—by muscarin, pilocarpin, saponin, apomorphin, potash salts in large doses, &c. Guanidin, physo.stigmin, and camphor will cause the heart to beat rhythmically after complete still-stand in diastole by muscarin.] On the theory that inhibitory ganglia are present in the heart, the following drugs— muscarin and physostigmin—by stimulating these ganglia cause arrest of heart’s beat in diastole, but the heart still contracts to a mechanical or electrical stimulus. These ganglia are depressed or paralysed by atropin, spartein, duboisin, hyoscyamin, daturin, as shown by the fact that stimulation of the vagus or the sinus venosus no longer arrests the heart’s action, nor does the application of muscarin cause any effect. Nicotin, saponin, and curare depress or paralyse the vagus-ends in the heart, as shown by the fact that stimulation of the vagus itself no longer slows or arrests the heart, while muscarin applied to the heart, or stimulation of the sinus venosus, will do so. Drugs, besides acting directly on the cardiac muscle, or its intra-cardiac nerve-ends and ganglia, may influence the heart in many other ways. One of these is by their action on the vagus centre in the medulla oblongata, as shown by the fact that if they stimulate this centre the slowing of the heart-beats thereby produced disappears after the vagi are cut. Amongst drugs acting in this way are digitalis and aconite (after Boehm and Brunton).'\ [Nature of a Cardiac Contraction.—The question as to whether this is a simple contraction or a compound tetanic contraction has been much discussed. So much is certain, that the systolic contraction of the heart is of very much longer duration (8 to 10 times) than the contraction of a skeletal muscle produced hy stimulation of its motor nerve. When the sciatic nerve of a nerve-muscle pre- paration is adjusted upon a contracting heart, a simple secondary twitch of the limb, and not a tetanic spasm, is produced when the heart (auricle or ventricle) contracts. This of itself is not sufficient j)i’oof that the systole is a simple spasm, for tetanus of a muscle does not in all cases give rise to secondary tetanus in the leg of a rheoscopic limb. Thus, a simple “ initial ” contraction occurs when the nerve is applied to a muscle tetanised by the action of strychnia, and the contracted diaphragm gives a similar result. The question whether the heart can be tetanised has been answered in the negative, and as yet it has not been shown that the heart can he tetanised in the same way that a skeletal muscle is tetanised.] [MacWilliain finds, when the quadriceps extensor cruris contracts to cause the knee-jerk, that a sound similar to the first sound of the heart is heard. As the former is regarded as a simple contraction, it is argued that a simple contraction can produce a muscle-sound. Fredericq$