THE CIRCULATORY SYSTEM. 



463 



Zinc. Sulphur is a mild alterative, valuable in rheumatism and 

 skin diseases, especially in the form of natural waters. Many 

 vegetable substances are credited with like properties, notably 

 Sarsaparilla, Guaiacum, Hemidesmus, Serpentary, and Mezer- 

 eum, but the physiological action of these is very obscure, and 

 their value as medicines doubtful. 



SYNOPSIS OF DRUGS WHICH INFLUENCE METABOLISM 



CHAPTER X. 



THE CIRCULATORY SYSTEM. 



I. PHYSIOLOGICAL RELATIONS. 



THE function of the heart is to drive a certain amount of blood 

 through the whole length of the circulatory system within a 

 given time. In its flow through the small arteries and 

 capillaries, the blood meets with great peripheral resistance, and 

 is dammed back, as it were, upon the larger arteries, which by 

 virtue of the elasticity of their coats are constantly distended, 

 and exert an equal and opposite pressure on the blood. The 

 intermittent action of the heart is thus converted into a 

 continuous force, the arterial blood-pressure, which (thanks to 

 the aortic valves) urges the blood forwards in a steady stream. 



