424 VEGETABLE DRUGS 



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 ventri- 

 cular dilatation ; at another time the heart beats rapidly and 

 siroi!g]y,when powerful systolic 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 and the heart 

 assumes various peculiar shapes (hour-glass, etc.). Death 

 usually occurs from cardiac arrest in systole, in which con- 

 dition it remains pale, firm and contracted, and unresponsive 

 to mechanical or electrical stimulation Rarely (men and 

 dogs) the heart stops in diastole. The action of digitalis on 

 the heart is more pronounced in dogs and sheep than in 

 horses and cattle. The characteristic 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 stimulation of the vagi, 

 ineffective before poisoning, will, after exhibition of digi- 

 talis, cause diastolic arrest of the heart. In regard to the 

 vessels, experiments conducted on the terrapin exhibit the 

 fact that when the vessels are deprived of their nerve 

 supply, the heart excised, and an artificial circulation sub- 

 stituted, 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 unaffected 

 save by toxic doses, and then through insufficient blood 

 supply, when the respiration becomes weak and imperfect. 



