448 VEGETABLE DKUGS ■ 



ventricles (pulse irregular). At one time the heart beats 

 slowly and weakly because the heart muscle can scarcely 

 overcome the tendency of the excited vagi to cause ventric- 

 ular dilatation; at another time the heart beats rapidly and 

 strongly, when powerful muscular contractions overmaster 

 the inhibitory influence of the vagi. The heart, during this 

 irregular toxic period, is seen to be unequally affected, in 

 that one portion (the apex) may be firmly contracted while 

 the rest of the ventricle is dilated. Moreover, the auricles 

 and ventricles do not act synchronously, owing to inhibition 

 of impulses from auricle, to ventricle. The irregularities 

 and rapidity of rhythm increase more and more (delirium 

 cordis), until both auricles and ventricles lapse into fibrillary 

 contractions, and death in mammals occurs in diastolic arrest. 

 The action of digitalis on the heart is more pronounced 

 in dogs and sheep than in horses and cattle. The char- 

 acteristic , 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 influenced. - That the peripheral vagi are 

 stimulated, is shown by the fact that an amount of galvanic 

 stiniulation of the vogi, ineffective before poisoning, will, 

 after exhibition of digitalis, cai^se diastolic arrest of the 

 heart. In regard to the vessels, experiments conducted on 

 the terrapin exhibit the fact that when the vessels are de- 

 prived of their nerve supply, the heart excised, and an arti- 

 ficial circulation substituted, even then vascular contraction 

 and retardation of flow will occur under the influence of 

 digitalin added to the factitious blood. The resultant of the 

 various actions of medicinal doses of digitalis is increased 

 work of the heart, so that more blood is pumped throughout' 

 the body in any given unit of time. 



Respiration.- — The respiratory centres are only influ- 

 enced by toxic doses, being first stimulated and then de- 

 pressed by digitalis: the respiration is first rapid and deep, 

 and later weak and imperfect. 



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