196 THE CONTRACTION OF CARDIAC MUSCLE. 



condition of complete contraction, till at length it is almost or quite 

 impossible to recognise the separate beats at all. 



Precisely similar curves can be obtained by the action of such drugs 

 as antiarine, veratrine, digitalin, which are known to act upon ordinary 

 striated muscle in a similar manner ; and it is of great interest for the 

 physiology of the heart, to find that muscarine solutions act in the 

 opposite direction, and produce a diastolic standstill of the same nature 

 as that produced by lactic acid. The opposing effect of the acid and 

 alkaline solutions can be seen in the same preparation, so that all the 

 intermediate steps between a systolic and a diastolic standstill can be 

 brought about by the administration of the alkaline solution, followed 

 by that of the acid solution, and vice versd. Precisely similar curves 

 can be obtained by the alternate administration of digitalin and 

 muscarine solutions, 1 so that we are, it seems to me, driven to the 

 conclusion that muscarine acts upon the apex of the ventricle, or upon 

 the whole ventricle, in the opposite sense to digitalin, and therefore, if, 

 as we have every reason to believe, digitalin produces its effect by 



FIG. 105. Beat of ventricle of frog registered by Gaskell's modification of Roy's tonometer. 

 Perfusion cannula in ventricle ; blood solution flowing through at constant pressure ; 

 at arrow, sodium hydrate solution was sent through instead of blood solution. 



FIG. 107. Same experiment as Fig. 106. After Fig. 106 had been obtained, blood solution 

 was sent through for seven minutes, and then at arrow the lactic acid solution was sent 

 through instead of the blood solution. 



direct action upon the muscle substance, in the direction of bringing 

 about a tonic condition of that muscle, muscarine must also directly act 

 upon the muscle in the opposite direction, and produce its effect by 

 bringing about an atonic condition of that muscle. This action of 

 muscarine will be considered further in a subsequent section. Of such 

 nature is the evidence that the cardiac muscle possesses tonicity as well 

 as rhythmicity. 



In addition to the evidence of the action of chemical substances, Fano 2 has 

 published evidence of another kind of tonic contraction which is more 

 mysterious and more difficult to understand. He finds that a clamp or 

 ligature placed in the auriculo-ventricular groove, will cause in Emys europcea 

 a rhythmical variation of tone in the auricles, of a most marked and striking 

 character. The phenomenon is confined to the auricles, and is not seen in any 

 other animal to the extent described in the case of Emys. The rate of rhythm 

 is not very regular ; the phenomenon, according to Fano, very often does not 

 appear until the beats of the auricle have been registered for a long time. It 



1 Gaskell, op. cit., Fig. 106, PI. III. 



2 " Ueber Tonuschwankungen der Atrien des Herzens von Emys europoea," Beitr. z. 

 Physiol. C. Ludwig z. s. 70 Geburtst. geic., Leipzig, 1887. 



