32 GENERAL ACTION OF DRUGS 



(c) Drugs increasing the force and rate of heart-heats. 

 Alcohol Strychnine 

 Chloroform Caffeine 



Ether Quinine 



Ammonia Arsenic 



Ammonium carbonate 



(d) Drugs decreasing the force and rate of the heart-heats. 

 Aconite Prussic acid 

 Veratrum viride Ergot 



Antimony salts 



The drugs most frequently given to animals for their action on the 

 heart are alcohol, ether, digitalis, strophanthus, ammonia, ammonium car- 

 bonate, camphor, caffeine, strychnine, atropine, aconite and veratrum 

 viride. The reader is referred to special articles on these drugs for 

 therapeutical indications and other details. 



III. — Drugs Acting on the Blood Vessels. 



The following table includes the mechanism regulating vascular 

 tension : 



Smooth muscular fibres 



1. In the walls of the vessels Terminations of vasodilators and 



vasoconstrictors 



2. Nerve supply of vessels Vasodilators 



Vasoconstrictors 



Vasoconstrictor or vasomotor centres 

 in the medulla and subsidiary cen- 



3. Centres tres in the spinal cord and sympa- 



thetic system, controlling the 

 constricting nerves 



Each peripheral vessel contains regulating, constrictor fibres, except, 

 possibly, those of the heart, lungs and brain. The vascular lumen is nar- 

 rowed by stimulation, and widened by inhibition, of the vasoconstrictor 

 apparatus. 



Some vessels possess dilating fibres which do not appear to be con- 

 trolled by a distinct center. But we cannot discriminate between the 

 action of a drug on the muscular fibres and the peripheral nerve endings 

 in the vessel walls ; nor can we always tell whether a drug acts to stimu- 

 late one set of peripheral fibres or depress the other. 



Vascular tension is increased not only by contraction of vessels, 

 but also by drugs which cause the heart to' beat more quickly, and by 

 those making its pulsations more forcible and complete, so that all the 

 blood is squeezed out of the ventricle at each contraction. Contrariwise, 

 blood pressure is diminished, not only by those drugs inducing vascular 

 dilatation, but by those reducing the rate or force of the heart, or both. 



We shall simply classify drugs influencing the vessels according as 

 to whether they act after absorption into the blood, or only when applied 

 locally to the vessel walls. 



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