120 CHEMICAL STIMULI. 



stimulus the contraction of the heart is the most vigorous possible. Hence, this 

 minimal electrical heart-stimulus is as effective as a maximal stimulus. 



V. Ziemssen was unable even with strong induction-currents to cause 

 a variation in the rate of the beat of the exposed human heart. The ventricular 

 diastole alone appeared to be no longer complete, and in addition certain minor 

 irregularities were observed in the contractions. By opening and closing or by 

 reversing a strong constant current applied to the heart of a woman, it was possible 

 to increase the number of heart-beats, and the increased number of pulsations cor- 

 responded with the number of the electrical impulses. For example, from a 

 normal of 80 the number of heart-beats was raised to from 120 to 140 to 180 

 by the application of from 120 to 140 to 180 electrical impulses. Conversely, it 

 was possible also to reduce the normal number of pulsations from 80 to 60 or 50 

 by applying an equal number of powerful stimuli. In the healthy subject also 

 v. Ziemssen found that he could influence the rhythm and the strength of the 

 heart by applying an electrical current through the chest-wall. 



(d) Chemical Stimuli. Many chemical agents, particularly when applied in a 

 state of dilution to the inner surface of the heart, increase the number of pulsa- 

 tions, but when applied in concentrated form or when allowed to act for some 

 time diminish the number or paralyze the heart. Bile and biliary salts diminish 

 the number of heart-beats, as does also absorption of the bile into the blood. 

 In dilute solution, however, both accelerate the action of the heart. The same 

 effect is produced by acetic, tartaric, citric and phosphoric acids. Chloroform and 

 ether when applied to the inner surface of the heart have a distinctly retarding 

 or even paralyzing effect; in small amounts ether accelerates the heart-beats. 

 Opium, strychnin, alcohol, and chloral hydrate have an analogous action. Klug 

 caused blood impregnated with various gases to pass through the frog's heart and 

 found that sulphurous acid, chlorin-gas, nitrous-oxid gas, hydrogen sulphid and 

 carbon monoxid acted as heart-poisons. In the same way, blood saturated with 

 carbon dioxid exhausts the heart, which, however, may recover if the carbon 

 dioxid escapes. A deficiency of oxygen produces a grouped rhythm, in the same 

 way as the phenomena of asphyxiation manifest themselves in the respiratory 

 apparatus in grouped movements. 



Rossbach found that local irritation of a circumscribed area of the frog's 

 ventricle by means of mechanical, chemical, or electrical stimuli during contraction 

 causes immediate relaxation in partial diastole of the part to which the stimulus 

 is applied. The immediate after-effect of this form of irritation is a permanent 

 shrinking of the irritated portion of the heart-fibers, and this is likewise strictly 

 confined to the area of irritation. The shrunken portion ceases to functionate 

 and remains permanently robbed of its vital properties. If the same stimuli are 

 applied during diastole, the irritated portion relaxes earlier than the portion that 

 has not been irritated, and the diastole of the irritated portion lasts longer than 

 that of the non-irritated portion. If the weakest stimuli are allowed to act for 

 a considerable length of time on any part of the frog's ventricle, the irritated 

 portion always relaxes earlier than the non-irritated, and the diastole of the 

 irritated portion lasts longer than that of the non-irritated. 



Heart- poisons comprise such substances as have a special effect in diminishing 

 or abolishing the movements of the heart. In this respect the neutral salts of 

 potassium are most remarkable. In small doses they accelerate the heart-beat. 

 Yellow potassium ferrocyanid, when injected into a frog's heart, will cause systolic 

 arrest of the ventricles, even when greatly diluted. If blood subsequently enters 

 the ventricle as the result of the contraction of the auricle, the ventricle may 

 again take part in the contraction. Under such conditions, the ventricular muscles 

 sometimes relax in areas after first undergoing reddening. The contraction of the 

 ventricle, which is exceedingly sluggish, later travels from the auriculo- ventricular 

 junction in a peristaltic wave to the apex. The Javanese arrow-poison, antiar, 

 causes systolic arrest of the ventricles, with diastolic arrest of the auricles; mus- 

 carin causes diastolic arrest of the heart, which can be overcome by means of 

 atropin. Some of the heart-poisons in small doses cause slowing and in larger 

 doses not infrequently acceleration of the heart -beat: digitalis (and the toxic 

 substances of oleander and the mayflower, which are similar to it), morphin, and 

 nicotin. Others in small doses cause acceleration and in large doses slowing: 

 veratrin, aconitin, camphor. 



