TOXIC ACTIONS 537 



the two factors, (1) contraction of muscular fibre, and 

 (2) stimulation of the inhibitory vagus roots in the medulla, 

 and of the nerve-endings in the heart itself. This represents 

 the therapeutic stage. 



2. Following these effects, there is often a stage of 

 excessive inhibition with very marked slowing of the 

 pulse, lessened outflow from the heart, and a temporary 

 fall of blood-pressure. 



3. Larger doses now bring about quickening of the heart 

 beat and a second rise of pressure, these effects being pro- 

 duced by paralysis of the vagus inhibition, and by a marked 

 increase in the irritability of the cardiac muscle. The 

 rhythm becomes quicker, but the auricles and ventricles 

 contract independently of each other, and the heart action 

 becomes very irregular. 



4. Still larger doses produce rapid fall of blood-pressure, 

 extreme irregularity of the heart (delirium cordis), sudden 

 stoppage of the heart, and death. The heart usually stops 

 before the respiration. 



Neither digitalis nor digitalin has any very direct action 

 on the brain or spinal cord, the stimulation being confined 

 to the medulla, nor any marked effect on sensory or motor 

 nerves. They temporarily quicken, and more notably 

 and permanently slow, respiration. By increasing general 

 blood-pressure, a somewhat fuller stream of blood passes 

 through the kidneys, and thus diuresis is tardily produced. 

 This is especially well marked in cases of valvular disease 

 of the heart. The venous congestion and stagnation of 

 blood in the kidney is relieved and fresh arterial blood is 

 pumped through it. No direct irritation of the kidneys 

 occurs ; but large doses, constricting arterioles, while at 

 the same time lessening the heart's force, diminish renal 

 excretion, and the drug consequently being longer retained, 

 its general effects are intensified, and its so-called cumulative 

 action developed. This can be avoided if the effects on the 

 circulation are not allowed to get beyond the therapeutic 

 stage. 



TOXIC ACTIONS. The toxic doses of the powdered leaves 

 are thus stated by Kaufmann : For horses, 400 to 480 

 grains ; for dogs, 80 to 130 grains ; for cats, 30 grains. 



