108 ACTION OF CHEMICAL STIMULI AND GASES ON THE HEART. 



fore, that the relation of the strength of the stimulus, to the extent of the contrac- 

 tion of the cardiac muscle, is quite different from what occurs in a muscle of the 

 skeleton, where within certain limits the amplitude of the contraction bears a 

 relation to the stimulus, while in the heart the contraction is always maximal.] 



(rf.) Chemical Stimuli. Many chemical substances, when applied in a dilute 

 solution, to the inner surface of the heart, increase the heart-beats, while if 

 they are concentrated or allowed to act too long, they diminish the heart-beats, 

 and paralyse it. Bile (Budge), bile salts (Rohrig) diminish the heai't-beats (also 

 when they are absorbed into the blood as in jaundice) ; in very dilute solutions 

 both increase the heart-beats (Landois). A similar result is produced by acetic, 

 tartaric, citric (Bobrik), and phosphoric acids (Leyden). Chloroform and ether, 

 applied to the inner surface, rapidly diminish the heart-beats, and then paralyse it; 

 but very small quantities of ether (1 per cent.) accelerate the heart-beat of the frog 

 (Kronecker and M'Gregor-Robertson), while a solution of 1| to 2 per cent, passed 

 through the heart arrests it temporarily or completely. A dilute solution of 

 opium, strychnia, or alcohol applied to the endocardium, increases the heart-beats 

 (C. Ludwig) ; if concentrated they rapidly arrest its action. Chloral-hydrate 

 paralyses the heart (P. v. Rokitansky). 



Action of Gases. When blood containing different gases was passed through 

 a frog's heart, Klug found that blood containing sulphurous acid rapidly and 

 completely killed the heart ; chlorine stimulated the heart at first, and ultimately 

 killed it ; and laughing-gas rapidly killed it also. Blood containing sulphuretted 

 hydrogen paralysed the heart without stimulating it. Carbonic oxide also 

 paralysed it, but if fresh blood was transfused, the heart recovered. [Blood con- 

 taining excites the heart (Castell), while the presence of much COo paralyses it, 

 and the presence of COo is more injurious than the want of 0. H and N have no 

 effect.] 



Rossbach found on stimulating the ventricle of a frog's heart at a circumscribed 

 area, either mechanically, chemically, or electrically, during systole, that the 

 part so stimulated relaxes in partial diastole. The immediate direct after-effect 

 of this stimulation is. that the muscular fibres in the part irritated remain some- 

 what shrivelled. This part ceases to act, and has lost its vital functions. If the 

 stimulus is applied during diastole, the part irritated always relaxes sooner, and 

 its diastole lasts longer than does that of the parts which were not stimulated. 

 If weak stimuli are allowed to act for a long time upon any part of the ventricle 

 of a frog's heart, the part so stimulated always relaxes sooner than the non-stimu- 

 lated parts, and its diastole is also prolonged. 



Cardiac Poisons are those substances whose action is characterised by special 

 effects upon the movements of the heart. Amongst these are the neutral salts of 

 potash. [Until 1863 it was believed that these salts were just as slightly active on 

 the heart as the soda salts, but Bernard and Grandeau showed that very small 

 doses of these salts produced death, the heart standing still in diastole. An 

 excised frog's heart ceases to beat after one-half to one minute when it is placed in 

 a 2 per cent, solution of potassic chloride.] Even a very dilute solution of yellow 

 prussiate of potash injected into the heart of a frog causes the ventricle to stand 

 still in systole. 



As early as 1691, Clayton and Moulin showed the poisonous action of potassium 

 sulphate, and alum, as compared with the non-poisonous action of sodium chloride, 

 which was demonstrated by Courten in 1679. Anliar (Java arrow-poison) causes 

 the ventricle to stand still in systole and the auricles in diastole. Some heart- 

 poisons in small doses, diminish the heart's action, and in large doses not unfre- 

 quently accelerate it e.g., digitalis, morphia, nicotin. Others, when given in 

 small doses, accelerate ita action, and in large doses slow it veratria, aconitin, 

 camphor. 



