ACTION OF DIGITALIS 425 



Nervous System and Muscles. — These are not influenced 

 b}' therapeutic doses of digitalis. Toxic quantities cause 

 ]oss of reflex action, muscular wenkness, and convulsions in 

 the frog. The first two phenomena are due to primary 

 stimulation of the inhibitory reflex centres of Setschenow in 

 the medulla, followed by general paralysis of the spinal 

 cord, and direct depression of the motor nerves and muscles ; 

 while the convulsions are caused by circulatory changes in 

 the base of the brain dependant upon the embarrassed 

 heart. 



Temperature. — 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 

 terminations is depressed and insensitive to the action of 

 the drug. 



Kidneys. — Metabolism and Elimination. — The influence of 

 digitalis on the amount of urinary secretion is uncertain. It 

 has no special action upon the mucous membrane or secret- 

 ing cells of the kidney. If general vascular tension is low- 

 ered (cardiac disease), digitalis will exert a diuretic action 

 in consequence of increasing blood pressure. As a rule, it 

 may be stated that if digitalis increases the systemic vascul.ir 

 tension more than that of the kidney, diuresis follows. The 

 effect of digitalis on tissue waste is uncertain and the mode 

 of its elimination is unknown. Experiments relative to the 

 composition of the urine are conflicting. The smooth mnscle 

 of the uterus is said to be stimulated to contraction by digi- 

 talis. 



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- 



