94 ACTION OF MEDICINES ON THE CIRCULATION 



order to promote free circulation in the superficial vessels, 

 and thus antagonise congestion of the internal organs. 



Cough depending upon gastric derangement, not un- 

 common in young animals, is often relieved by antacids. 

 Cough resulting from bronchial filariae is abated by the usual 

 soothing remedies, and sometimes removed by turpentine 

 administered in drench or intratracheally, or by inhalation 

 of diluted chlorine, vapour of iodine, or sulphurous acid, 

 which is rendered still more effectual for destruction of the 

 parasites when conjoined with carbolic vapour. 



In dogs with bronchitis or pneumonia, when the breathing 

 is difficult, relief is often obtained by giving an emetic of 

 ipecacuanha and squill. Venous congestion is overcome, 

 and the state of the bronchial secretions improved. These 

 good effects may often be maintained by the subsequent use 

 of frequently repeated doses of ammonium carbonate, which 

 is also serviceable earlier, or when the patient is too weak to 

 justify the use of an emetic. In dogs recovering from acute 

 attacks, or suffering from chronic bronchitis, cod liver oil 

 is often useful, possibly on account of its furnishing readily 

 assimilable nourishment for the delicate epithelial cells. 



ACTION OP MEDICINES ON THE CIRCULATION 



Medicines can affect the circulation by acting on either the 

 heart or the vessels. There are many ways in which the 

 heart can be affected, and it must be remembered that 

 normally the rhythm of the heart is under the control of two 

 sets of nerves, namely the vagus and the sympathetic. The 

 vagus has its centre in the medulla and its fibres end in the 

 heart wall, where they connect with the intra-cardiac ganglia 

 from which non-medullated fibres ramify in the heart wall. 

 Whether stimulated Centrally or peripherally the vagus 

 causes inhibition, slowing the beat and lessening the heart 

 force. The sympathetic has the reverse effect, and stimula- 

 tion quickens and strengthens the heart beat. But in 

 addition to these direct nervous effects, any changes in blood 

 pressure affect the cardiac rhythm, a fall in pressure producing 

 a quicker pulse and vice versa. Then again cardiac muscle 

 is directly acted on by several drugs, some strengthening and 



