2 2 2 THE CONTRA CTION OF CARD I A C MUSCLE. 



The action of curari is upon the motor end-plate of the ordinary striated 

 muscle, and takes the place of atropine in cases where the muscle becomes 

 striated in character ; thus in the bird's pupil, where the fibres are striped, 

 curari not atropine causes dilatation. In the oesophagus of various mammals 

 where the muscle is partly striped, partly unstriped, atropine prevents the 

 action of the nerve on the unstriped, curari on the striped muscle ; and, 

 curiously enough, in the hearts of the snail, octopus, etc., according to 

 Ransom's l observations, where the muscle is not only markedly striped, but 

 also varies in strength of contraction according to the strength of stimulus, 

 and can be tetanised, the action of the inhibitory nerve is not affected by 

 atropine, but is put out of play by curari. In all these cases the curari in all 

 probability acts on the endings of the nerve in the muscle. In the case of the 

 heart of the frog and toad, and doubtless of other vertebrate hearts, the 

 curari acts like nicotine on the junction of the pre-ganglionic fibre with the 

 nerve cell, before it acts upon the junction of the post-ganglionic fibre with 

 the muscle. 



Atropine prevents the action of the motor nerves on the unstriped muscle 

 of the oesophagus, of the iris, of the secretory nerves of the gland cells, whether 

 sweat glands or salivary, of the inhibitory nerves of the heart of vertebrates, 

 and from its local action it is clear that it paralyses the post-ganglionic fibres 

 as well as the pre-ganglionic. In addition, it appears to act upon the muscle 

 fibre itself. 



The removal by atropine of Bowditch's " staircase " phenomenon, of the 

 " local diastole " of Schiff, of the inhibitory action of the interrupted current 

 on the strip from the tortoise auricle, are all to be explained by the action of 

 the drug 011 the terminations of the post-ganglionic fibres in the muscle. On 

 the other hand, Eansom 2 has shown that, in the case both of the cephalopod 

 and of the snail, atropine must be classed with drugs, such as digitalin, antiarine, 

 etc., which produce an increased tonic contraction of the cardiac muscle. 

 Romanes 3 has shown the same thing with respect to the muscular tissue of 

 the Medusce, and I myself, in my investigations on the action of various drugs 

 on the apex of the frog's ventricle, 4 came to the conclusion that atropine acts 

 in a much less degree but in the same direction as those drugs which increase 

 the muscular contraction, and diminish relaxation. 



The direct action of atropine upon the muscle-substance is rendered 

 probable by its antagonising action to drugs which weaken muscular 

 contraction by their direct action upon muscle. 



This is especially seen in the case of such poisons as muscarine, 

 which is apparently a muscle-poison, not a stimulant to inhibitory 

 fibres or inhibitory mechanisms. 



We see from the evidence brought forward by Luchsinger and his 

 pupils, 5 that a series of substances, such as potash salts, and the whole 

 group of substances containing trimethyl-ammonium, to which muscarine 

 belongs, all act in the same way upon the muscular tissue of the heart, 

 namely, in the direction of weakening the contractions, and ultimately 

 bringing the muscle into the condition of diastolic standstill ; all behave, 

 in fact, in the^same manner as lactic acid, according to my observations. 

 In opposition to this series of substances, we find another series which 



1 Journ. PhysioL, Cambridge and London, 1885, vol. v. p. 261. 



" Op. cit., pp. 301, 331. 



3 Phil. Trans., London, vol. clxvii. p. 736. 



* Journ. Phywol., Cambridge and London, 1880, vol. iii. p. 14. 



5 Luchsinger and Am. Clause, ' ' Zur Kenntniss der Hemmungsmechanismen des 

 Herzens," Inaug. Diss., Bern, 1884; Olga Sokolow, " Physiol. u. toxikolog. Stiulien am 

 Herzen," Inaug. Diss., Bern, 1881. 



