96 ON THE NATURE AND ACTION OF THE 



finding that, in ordinary cases of poisoning, the cardiac action 

 may be maintained by the use of artificial respiration for more 

 than thirty hours, as Mr. Richards has succeeded in doing in 

 India. The cardiac movements cease much sooner in frogs 

 poisoned by cobra-venom than in those paralysed by curare — 

 the pulsations in the latter often continuing for very many 

 hours, or even for one or two days. They are also arrested by 

 the direct application of the poison to the heart, as in Experi- 

 ment LXXII. Its action seems to be somewhat different in 

 degree, if not in kind, when applied to the outside of the heart, 

 as in Experiment LXX, and to the inside, as in Experi- 

 ment LXXII ; for in the former case the pulsations continued 

 for a considerable time, while in the latter they were instantly, 

 arrested, the heart stopping in partial systole and moderately 

 contracted. 



Tiie action of cobra-poison being exerted on the lieart of the 

 frog after its excision shows that it acts on the heart itself; 

 and its effect heiug very much the same without the body as 

 within it renders it probable that the central nervous system is 

 little concerned in the arrest of circulation by the poison, at 

 least in the frog. 



The stoppage of the excised heart may be due (1) to irritation 

 of the inhibitory centres contained within it, or (2) to paralysis 

 of its motor ganglia, or (3) to excessive stimulation of them 

 producing tetanus, or (4) to the action of the poison on the 

 muscular fibre of the organ. It is not due to the first of these 

 causes ; for atropia, which paralyses the inhibitory ganglia, does 

 not restore the movements. The second is improbable, as the 

 heart does not stop in diastole but in systole, and resists 

 distention by fluid within it. The third seems the most 

 probable cause, as one does not see why the poison should 

 arrest the cardiac pulsations at once when applied to the 

 interior of the organ, and not do so when placed on the 

 outside, if it acted on the muscular fibre, whereas it may 

 readily be supposed that the poison may reach the ganglia 

 more readily from the inner side of the heart — though we do 

 not venture to assert that this is the true explanation of the 

 facts we have observed. 



