ACTION OF DIGITALIS 423 



Dose.— H. &a, lii.-vi. (60.-180.); Sh. & Sw., § ss.-i. (15.-30.); D., 

 3 i.-iv. (4.-15.). 



ACTION OF DIGITALIS. 



External. — None. 



Internal. — Alimentary Canal. — Digitalis in large doses is 

 a gasiffo-intestinal irritant, and in poisoning causes nausea, 

 colic, purging, and vomiting in animals capable of the act. 



Circulation. — The dominant action of digitalis is ex- 

 pended upon the heart and blood vessels. After medicinal 

 doses we find the pulse becomes : 1. Slower. 2. Fuller and 

 stronger. 3. More regular in rhythm, if previously irregu- 

 lar. In poisoning, these phenomena are reversed and the 

 pulse is : 1. Eapid. 2. Weak. 3. Irregular. The thera- 

 peutic effects following moderate doses are due to: 1. 

 Stimulation of the heart muscle, and perhaps its con- 

 tained ganglia (pulse stronger and somewhat less frequent). 

 2. Excitation of the vagus centre and the vagus cardiac 

 terminations (pulse infrequent). 3. Stimulation of the mus- 

 cular walls of the vessels and vasomotor centres (increased 

 vascular tension). The tension is also augmented by the 

 greater force of the heart beat, and, on the other hand, 

 the heart is slowed in overcoming the increased resistance 

 in the vessels. In consequence of the action on the heart 

 the ventricular contractions are complete and forcible, and 

 the diastolic period is lengthened; therefore, more blood 

 enters the viscus and more is squeezed out with each con- 

 traction. The systolic period is unaltered. Furthermore, 

 the nutrition of the heart is thought to be promoted by: 

 1. Increase of its blood supply during the prolonged dia- 

 stole. 2. Stimulation of the trophic nerves (vagi?) of the 

 heart. As diastole is the rest period of the heart, increasing 

 it conserves the strength of the organ. In poisoning, the 

 symptoms noted above follow: 1. Paralysis of the peri- 

 pheral vagi (pulse rapid). 2. Insufficient filling of the vessels 

 and paralysis of the vessel walls (low tension). 3. Forcible 

 contractions contending against prolonged dilatation of the 



