DEUGS WHICH ACT ON THE HEART AND BLOOD-VESSELS 461 



Action and Uses. — A tonic effect upon the heart is claimed for 

 digitalis, as it increases the force of its contractions while lessening their 

 number. By stimulating the nerves which contract the blood-vessels a 

 better tone is imparted to them, and the circulation is rendered more 

 efficient. Strength is given to the feeble heart, and when irregular or 

 intermittent, it is made to act in a steady and rhythmic manner. It is 

 found to have a beneficial effect in horses for a short time, but its con- 

 tinued administration results in irritation of the stomach and inappetence. 

 Poisonous doses act by causing spasm of the heart and consequent death 

 from cardiac paralysis. Digitalis excites the kidneys to excrete a larger 

 amount of urine than usual, and for this reason it is employed in the 

 removal of dropsical swellings. 



It is also given in combination with other drugs in cases of chronic 

 cough, and with apparently beneficial results. 



Strophanthus is the plant from which the arrow poison is derived, 

 and its action in large doses is to paralyse the heart and other involuntary 

 muscles. It is more soluble and rapid in its action than digitalis, but its- 

 effects are not so enduring. Continued administration, however, is less 

 often attended with gastric disturbances. There are some cases of valvular 

 trouble for which digitalis is unsuited, but in which strophanthus may be 

 used with advantage. 



HEART SEDATIVES 



Remedies which diminish both the force and frequency of the heart- 

 beats, thereby producing a soothing efl'ect, are called heart sedatives. By 

 their depressing effect upon the heart they may be said in a certain sense 

 to weaken its action, and if given without judgment are very dangerous. 

 In the case of plethoric horses with high temperatures, aconite is given ta 

 slow the heart's action, but is not persisted in. Aconite, hellebore, and 

 antimony are the chief drugs of this class. 



Aconite. — The monk's-hood (Aconitum Napellus) is the plant from 

 which the Pharmacopoeia preparations of this drug are made. They are 

 aconitine — the active principle, — extract, tincture, liniment, and ointment. 



Judging from the behaviour of horses, we may conclude that aconite 

 applied to the more sensitive portions of the skin — the tongue and mouth 

 generally — produces the tingling sensation so noticeable when brought in 

 contact with similar parts on ourselves. The sensibility of the nerve ends- 

 being reduced by aconite, advantage is taken of the fact to employ lini- 

 ments and ointments containing it with the object of allaying pain in acute 

 rheumatism and painful swellings of various kinds, provided always that 

 the skin is not abraded. When given internally, the effect upon the heart 



