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.

Landois, L. (Leonard), 1837-1902. Lehrbuch der Physiologie des Menschen. English

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.

137/602 page 97

$level', such as a straw. Tlie slide is warmed by means of a spirit-lamp. In this way the frequency and amplitude of the contractions are readily made visible at a distance.] (b) Mechanical Stimuli.—Pressure applied to the heart from without accelerates its action. In-the case of Frau Serafin, v. Ziemssen found that slight pressure on the auriculo-ventricular groove caused a second short contraction of both ventricles after the heart-beat. Strong pressure causes a very irregular action of the cardiac muscle. This may readily be produced by compressing the freshly excised heart of a dog between the fingers. The intra-cardiac pressure also affects the heart-beat (p. 95). If the pressure within the heart be increased, the heart-beats are gradually increased ; if it be diminished, the number of beats diminishes {Ludwig and Thiry). If the intra-cardiac pressure be very greatly increased, the heart's action becomes very irregular and slower. A heart which has ceased to beat may under certain circumstances be caused to execute a single contraction if it be stimulated mechanically. (e) Electrical Stimuli.—A constant electrical current of moderate strength increases the number of heart-beats. V. Ziemssen found, in the case of Frau Serafin (§ 47, 3), that the number of beats was doubled while a constant uninterrupted strong current was passed through the ventricles. [If the con- stant current be very strong, or if tetanising induction cur- rents be applied to the heart, e.g., of a dog, the normal heart-beat C Fig. 74. A, contraction of a frog's heart at 19° C. ; B, at 34° C. ; C, at 3° C. is abolished, the ventricular muscle being thrown into a state of irregular, arhythmic contrac- tion, whilst there is a great fall of blood-pressure {Ludtvig and Hoffa). This condition is spoken of as delirium cordis or fibrillar contraction. It is caused by some change in the muscular fibres of the ventricles themselves ; the movements are very complex, last long, and occur rapidly ; the persistence seems to be due to the great excitability of the ventricular tissue. It appears to consist of a rapid succession of inco-ordinated peristaltic contractions, which may be brought about as described above, or by the action of some depressing agents, e.g., potassic bromide. These ventricular fibrillar contractions are not affected by stimulation of the vagus. Similar electrical stimulation of the auricles causes a fluttering movement, more like a series of contractions, without any distinct sign of inco-ordination. These auricular movements are arrested by stimulation of the vagus {Mac William).^ If the auriculo-ventricular groove be compressed so as to cause the ventricle of a frog's heart to cease to beat, on placing one elec- trode of a constant current on the ventricular wall and the other electrode on an indifferent part of the body, we obtain, on making the current, a systolic contraction of the ventricle only when the cathode touches the ventricle ; and conversely on breaking, only when the anode is on the heart {Biedermann). When a single induction shock is applied to the ventricle of a frog's heart during systole, it has no apparent effect ; but if it is applied during diastole, the succeeding contraction takes place sooner. The auricles and also the apex behave in a similar manner. Whilst they are contracted, an induction shock has no effect ; if, however, the stimulus is applied during diastole, it causes a contraction, which is followed by systole of the ventricle. Even when strong tetanising induction shocks are applied to the heart, they do not produce tetanus of the entire cardiac musculature, or, as it is said, the heart knows no tetanus {Kronecker and Stirling). Small white, local weal-like elevations—such as occur when the intestinal musculature is stimulated—appear between the electrodes. They may last several minutes. A frog's heart, which yields weak and irregular contractions, may be made to execute regular rhythmical con- tractions synchronous with, the stimuli, if electrical stimuli are used {Bowditch). [Break induction shocks, if of sufficient strength, cause the heart to contract, while weak stimuli have no eff'ect; on the other hand, moderate stimuli, when they do cause the heart to contract, always cause a maximal contraction, so that a minimal stimulus acts at the same time 7$