ACTION OF CHEMICAL STIMULI AND GASES ON THE HEART. 85 



(Kronccker). It is quite clear, therefore, that the relation of the strength of the stimulus to 

 the extent of the contraction 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.] 



Human Heart. V. Ziemssen found that he could not alter the heart-beats of the human 

 heart {Fran Serafin, 47, 3), even with strong induction-currents. The ventricular diastole 

 seemed to be less complete, and there were irregularities in its contraction. By opening and 

 closing, or by reversing a strong constant current applied to the heart, the number of beats 

 was increased, and the increase corresponded with the number of electrical stimuli ; thus, when 

 the electrical stimuli were 120, 140, 180, the number of heart-beats was the same, the pulse 

 beforehand being 80. The normal pulse-rate of 80 was reduced to 60 and 50 when the number 

 of shocks was reduced in the same ratio. [In Frau Serafm's case the electrodes were applied to 

 the heart, separated from it merely by the pericardium. Ziemssen found that the Faradic 

 current did not modify the heart's action when the thorax was intact, but that the constant 

 current did; if of sufficient strength. Herbst and Dixon Mann obtained negative results with 

 both kinds of electricity in the normal thorax.] 



(d) 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, and bile salts, diminish the 

 heart-beats (also when they are absorbed into the blood as in jaundice) ; in very dilute solu- 

 tions both increase the heart-beats. A similar result is produced b}^ acetic, tartaric, citric, and 

 phosphoric acids. 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 {Kronccker and M l Gregor -Robertson), while a solution of 1^ to 

 2 per cent, passed through the heart arrests it temporarily or completely. Dilute solutions of 

 opium, strychnia, or alcohol applied to the endocardium, increase the heart-beats ; if concen- 

 trated they rapidly arrest its action. Chloral-hydrate paralyses the heart. 



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 

 containing O excites the heart {Castell), while the presence of much C0 2 paralyses it, and the 

 presence of C0 2 is more injurious than the want of O. Blood or serum completely saturated 

 with C0 2 exhausts the heart {Saltet and Kronccker), but it recovers itself when the C0 2 is 

 removed. H and N have no effect.] 



Cardiac Poisons are those substances whose action is characterised by special effects upon the 

 movements of the heart. Amongst these are neutral potash salts, which cause the heart to 

 stand 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. 

 Antiar (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 unfrequently accelerate it, e.g., digitalis, morphia, nicotin. Others, when given in small 

 doses, accelerate its action, and in large doses slow it veratria, aconitin, camphor. 



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 aidomatic ganglia, 

 some toxicologists assume 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 and Koppe). [According to Gaskell, 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 thSse 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 atropine 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 atropine. The cardiac muscle itself 

 remains excitable after the action of muscarin and iodine-aldehyd, so that if it be stimulated 



