DIGITALIS 333 



irregularities and rapidity of rhythm increase more and more (delirium 

 cordis), until both auricles and ventricles lapse into fibrillary contrac- 

 tions, and death in mammals occurs in diastolic arrest with dilatation to 

 the extreme limit. Recent work shows that in the last stage of poisoning 

 by digitalis irritability of the heart muscle accounts for the acceleration 

 of the heart, while the fact that ,pne pair of chambers is acted upon more 

 readily than the other pair explains the arrhythmia. The nutrition of 

 the heart is improved by digitalis in various ways. The coronary arteries 

 are filled from the aorta with the most highly oxygenized blood in the 

 body, during ventricular systole, but their finer ramifications are supplied 

 during diastole. Digitalis increases pressure in the aorta and prolongs 

 diastole, both augmenting coronary flow. The more forcible systole aids 

 in completely emptying the coronary veins. Experimentally digitalis 

 solution flowing through the coronaries constricts them. But it is highly 

 improbable that this happens with clinical doses, while digitonin (also 

 adrenalin and caffeine) has been found to actually dilate coronary vessels. 

 The normal pulsations of the heart and arteries create a kind of self- 

 massage of these parts, causing a sucking in and expulsion of blood and 

 lymph through the vessels of the heart and arteries — a process vital to 

 their nutrition. Drugs stimulating the circulation (digitalis) thus greatly 

 increase the self-massage and nutrition of the heart and vessels. 



It must be especially emphasized here that the peculiar and benefi- 

 cent action of the digitalis series is due mostly to its action in directly 

 stimulating the heart muscle which results in this organ doing two and 

 one-half times its usual work (Gottlieb and Magnus). 



In the frog the action of digitalis in exciting cardiac contractions is 

 much more marked than in mammals. Here the ventricular contractions 

 become longer and stronger and the rest periods shorter and weaker 

 until in lethal poisoning the heart stops in one prolonged systole with 

 complete obliteration of the ventricular chamber. The physiologic stand- 

 ard consists in 0.007 Gm. digitalis per Gm. of frog causing systolic arrest 

 of the heart. The slowing of the rhythm in the frog is due to prolonged 

 systole. In mammals slowing in rhythm is due to both prolonged systole 

 and diastole, mainly the latter. • 



Slowing of the heart owing to increased diastolic rest would naturally 

 diminish the total output of the heart but with medicinal doses of digitalis 

 the stimulating effect on the heart muscle is much more marked than 

 vagus stimulation. When diastole is much prolonged by an over-dose of 

 the drug then the total output of the heart is actually lessened. In the 

 normal mainmalian heart dilatation of the ventricles is favored by digi- 

 talis but, in the heart dilated by disease, the dilatation may be overcome 

 by the drug's action in stimulating the heart muscle. 



- The action of digitalis on the heart is more pronounced in dogs and 

 sheep than in horses and cattle. The characteristic effect of digitalis is 

 observed when it is applied locally to the isolated nerve-free apex, or 

 when the vagi are previously cut or paralyzed by atropine, and when the 

 spinal cord is destroyed. These facts show that the heart muscle is influ- 

 enced. That the peripheral vagi are stimulated, is shown by the fact that 

 an amount of galvanic stimulation of the vagi, ineffective before poisoning, 



Digitized by Microsoft® 



