ACTION OF DIGITALIS 449 



Nervous System and Muscles. — These are not influenced 

 "by therapeutic doses of digitalis. Toxic quantities cause 

 loss of reflex action, muscular weakness, vomiting, and con- 

 vulsions in the frog. The first two phenomena are due to 

 primary stimulation of the inhibitory reflex centres of Set- 

 schenow in the medulla, followed by general paralysis of the 

 spinal cord, and direct depression of the motor nerves and 

 muscles ; while the convulsions are also caused by stimulation 

 of the medulla. 



Temperaiiire. — The temperature is unaffected by medi- 

 cinal doses. Toxic doses reduce temperature. Fever is 

 lowered by large doses of digitalis, but it is rarely safe to 

 use the drug as an antipyretic. Moreover, digitalis is some- 

 times inoperative as a heart stimulant in fever, because the 

 functional activity of the vagus centres and peripheral term- 

 inations is depressed and insensitive to the action of the 

 drug. 



Kidneys.— Metaholism and Elimination. — The influence 

 of digitalis on the amount of urinary secretion is variable. 

 It may exert a slight stimulating effect upon the renal secret- 

 ing cells. (Albumin and blood in urine in poisoning.) If 

 general vascular tension is lowered (cardiac disease), dig- 

 italis will exert a diuretic action in consequence of increas- 

 ing blood pressure. As a rule, it may be stated that if 

 digitalis increases the systemic vascular tension more than 

 that of the kidney (stimulating pressure in glomerules), 

 diuresis follows. TIhe effect of digitalis on tissue waste is 

 uncertain and the mode of its elimination is unknown. Ex- 

 periments relative to the composition of the urine are 

 conflicting. The smooth muscle of the uterus is said to be 

 stimulated to contraction by digitalis. 



Cumulative Action. — Digitalis and strychnine are said 

 to be cumulative in their action. Evidence is stronger in the 

 case of the former drug than in that of the latter. By cumu- 

 lative action is meant sudden transition from a therapeutic 

 to a toxic effect. This may be due to three causes. 1. Tardy 

 absorption. 2. Increasing susceptibility. 3. Delayed elim- 



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