458 HEALTH AND DISEASE 



blood and perfect vessels by which to convey the life-fluid to all parts of 

 the body, and yet perish, if the heart fails in its work as a central pumping 

 station, or if the blood-vessels of one organ are surcharged, while the 

 nutrient supply fails to reach others. 



The causes of disordered circulation are irregularities of the heart, 

 whose contractions may be too forcible, too feeble, or irregular; or the 

 heart may be capable of doing its work efficiently, but the vessels may 

 offer undue resistance by reason of their calibre being abnormally con- 

 tracted; or, on the other hand, they may be so far relaxed as to permit too 

 free a flow of blood to a particular organ, causing congestion. 



Kemedies which affect the heart and blood-vessels are therefore of great 

 importance, and deserve careful consideration. 



HEART STIMULANTS 



It has been elsewhere explained that the heart is a muscular organ 

 which, by its contractions, propels the blood over the body. If it contracts 

 with inadequate force the cavities are not properly emptied, nor the blood- 

 vessels filled, and nutrition is impaired. If by shock or haemorrhage an 

 insufficient blood-supply is sent to the brain, its functions are suspended, 

 and the animal faints and falls. The recumbent position thus assumed 

 is favourable to recovery, and with removal of the cause the heart's action 

 may be restored. When syncope threatens a horse he staggers, and in 

 trying to keep upon his feet gives us some warning of his condition, which 

 it is well to heed for his sake as well as our own safety. Trembling, 

 sighing, and staggering will be noticed, and an examination of the mem- 

 branes shows them to be blanched, or pallid, like the countenance of a 

 person about to swoon. If a heart stimulant is given, the function of the 

 organ will probably be restored for the time, and the brain again recovering 

 its due supply of blood, consciousness w r ill return. 



Any failure of the heart acts upon its own substance, which, like every 

 other part of the body, derives its nourishment from the blood. 



The heart receives its stimulus through the nervous system, and it has 

 within it certain minute nervous bodies (ganglia) designed to excite and 

 cany on the rhythmic movements which are commonly called "beats". 

 Kemedies which influence the beats of the heart do so through these nerve- 



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centres being acted upon by agents which have entered the blood-stream. 

 They are further controlled by the pneumogastric nerve, which slows the 

 action of the organ, and by the sympathetic nerves, which excite it; and it 

 is through the medium of these that stimulants are able to increase both 

 the frequency and the force of the muscular contractions. 



