

THE CIRCULATION. 333 



of respiration. Changes also take place in the epithelium of the 

 alveolus. 



Cardiac Pain. Pain in the heart is due to disease of the coronary 

 arteries and of the origin of the aorta. 



Excess of Circulating Fluid. The continuous drinking of large 

 quantities of water may cause the heart to increase its systolic force to 

 overcome the increased amount of circulating fluid but finally it may 

 fatigue itself, weaken and cease acting. Hence an excess of drinking of 

 fluid is injurious in weakness of the muscular structure of the heart. 



Effect of Various Conditions. Exercise, mental work, rage and 

 cold elevate blood-pressure; the last two causes often produce 

 apoplexies. Heat, rest and sleep depress the arterial tension. 



Pharmacological. Adrenalin greatly elevates blood-pressure by 

 an action on the muscular structure of the arterioles, or, according 

 to Langley, by an action on the myoneural substance. Amyl nitrite 

 or nitroglycerine lowers arterial tension chiefly by an action on the 

 walls of the arterioles. Adrenalin, when given with nitroglycerine, 

 overcomes its action on blood-pressure. 



Urea increases arterial tension by an irritation of the vasocon- 

 strictor center. On the vessels of the kidney urea acts locally as a 

 vasodilator. 





