HEART TONICS 97 



and prevent or relieve congestion. Horses brought in chilled 

 and exhausted are frequently saved from congestion and 

 inflammation of internal parts by the timely use of a stimu- 

 lating drink, the good effects of which are further ensured 

 by an extra rug, and flannel bandages to the legs. More 

 permanent dilatation of external vessels is effected by fre- 

 quently repeated doses of nitrous ether and ammonium 

 acetate, with which camphor may also be conjoined. In 

 combating chronic inflammation, vascular dilators are also 

 serviceable, and their operation is further promoted by hot 

 applications, friction, and counter-irritation. 



HEART TONICS produce their effects more gradually and 

 slowly than heart stimulants. Although large doses may 

 induce violent, excitable, irregular heart action, repeated 

 moderate doses prolong the diastole, and render the con- 

 tractions slower, stronger and more regular. Most, besides, 

 contract the muscular coat of the arteries, and hence are 

 vascular tonics. On the muscular coat of the digestive 

 canal they are also liable to act, producing nausea, spasms, 

 and sometimes diarrhosa. Heart tonics comprise digitalis 

 and its constituents, sparteine, cactus, strophanthus, vera- 

 trine, convallaria majalis, squill, nux vomica, and strych- 

 nine. 



Digitalis has hitherto been the heart tonic generally used, 

 notwithstanding the disadvantage of its preparations being 

 of irregular strength, and its active principles, digitalin and 

 digitoxin, usually consisting of several bodies, differing con- 

 siderably in their actions. The difficulty is overcome only 

 by physiological standardisation of the drug and its prepara- 

 tions. Digitalis is prescribed where one or other ventricle, 

 from weakness and dilatation caused by reducing disease, 

 or from incompetence of the auriculo-ventricular valve, is 

 unable to drive the blood into the arteries. In hard- 

 worked horses compensating hypertrophy gives increased 

 propelling power, and hence sometimes mitigates the results 

 of valvular disease. When dilatation occurs, and the mitral 

 valve is insufficient to close the orifice, blood is liable to 

 regurgitate into the left auricle, retarding the blood flow 

 from the lungs, and leading to general venous congestion. 

 Heart tonics, notably digitalis, relieve this condition by 



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