14 



atropine on the arrhythmias of the disease 

 have been very interesting. As the result of 

 a large number of cases we have concluded 

 that the dromotropic action of that remedy is 

 very marked and that its habitual chrono- 

 tropic action is very small and even unap- 

 preciable in many cases. Here in some way 

 there occurs the physiologic dissociation of 

 the fibers of the vagus, and the atropine acts 

 predominantly on those that interfere in the 

 conductibilily of the cardiac mnscle. 



Several cases of complete block, others 

 of partial block and many of extrasystoles 

 were the subject of the experiment. 



In complete block the dromotropic 

 action of the remedy was nil and the inde- 

 pendence between the sino-auricular and 

 ventricular rhythms remained unaltered. In 

 the same cases the chronotropic action made 

 itself felt very slightly, and often in a 

 negative sense, that is, by causing the par- 

 adoxical effect of diminishing the number 

 of beats of the auricle. 



The experiments relative to partial block 

 were of greater interest. In this case the 

 elective action of the atropine on the con- 

 ductibility was notable. In the majority of 

 the experimented cases the remedy regulat- 

 ed the rhythm, that is, normalized the defic- 

 ient conduction. The chronotropic action 

 was unappreciable or at times acted in a 

 negative sense, diminishing the number of 

 auricular beats. 



How is the restoration of conduction 

 by atropine in the cases of heart block to 

 be interpreted? Must the nervous origin of 

 the alterations of conductibility be admitted 

 here? No. The muscular nature of such al- 

 terations is clear and is demonstrated by 

 the direct proof of the lesions of the myo- 

 cardium. Furthermore, the cases of complete 

 block, which represent only a more advanced 

 degree of arrhythmia and whose pathogene- 

 sis is identical to theirs, was not modified 

 by the action of the atropine, which ex- 

 cludes the entirely nervous nature of the dis- 

 turbance of rhythm. 



No doubt could exist about the only 

 possible interpretation of these results. The 

 lesions of His' bundle make it more excit- 

 able and give rise to the increase of phys- 

 iologic tone of the vagus with the conse- 

 quent alterations of conductibility that can 

 be corrected by atropine, If these lesions 

 were more intense, the atropine would not 

 act in the same way, for there the block is 

 already independent of the nervous action 

 and is associated exclusively with the patho- 

 logic process of the muscle. 



Moreover, the influence of anatomic 

 changes of the conducting bundle on the 

 inhibiting effects of the vagus is demonstrat- 

 ed in the experiments on the action of 

 digitalis, although in a sense antagonistic 

 to that referred to the action of atropine. 



According to Mackenzie, digitalis exerts 

 no action on the conductibility of normal 

 beats, but with the presence of lesions of 

 the muscle that remedy, even in a thera- 

 peutic dose, increases the time of conduct- 

 ion of the sinus stimulus to the ventricle, 

 eventually producing partial block. We 

 know of no case reported of total digitalis 

 block in man, and therefore the importance 

 of one of our cases iucreases in which the 

 action of crystallized digitalin determined 

 the appearance of a total block with the ner- 

 vous symptoms of the syndrome. When the 

 use of the remedy was suspended, the total 

 block was transformed into a partial one, 

 and the radial pulse rose from 35 to 50. 

 Simultaneously the nervous symptoms disap- 

 peared and other symptoms associated with 

 the block diminished. However, in this case 

 the action of the digitalis caused a consider- 

 able increase of the vagus tonus on the in- 

 jured His' bundle. When the use of the rem- 

 edy was stopped, the altered dromotropic 

 function returned to its former condition. 



It is, without doubt, less easy to inter- 

 pret the paradoxical effect of the atropine on 

 the chronotropic function, especially apprec- 

 iable in the cases of partial block. Similar 

 facts are reported in the medical literature 

 in cases of alteration of heart rhythm; but 



