514 THE OUTGO OF ENERGY 



When the pressure rises in the ventricle to a suffi- 

 cient height the contents of the ventricle will be dis- 

 charged through the aortic valve into the aorta, and 

 thus (through a convenient metal tube) into the 

 arterial tube, leading to the capillary resistance. 

 Here two paths may be taken : the liquid may pass 

 either through the capillary channels in the cane, thus 

 meeting with a high resistance, or this resistance may 

 be lessened to any desired degree by unscrewing a 

 clamp and thus opening the side tube. Both paths 

 lead to the venous tubes, whence the liquid passes 

 through the mitral valve into the ventricle. The 

 mitral and aortic valves are of a modified Williams 

 type. Metal tubes closed at one end conduct the 

 liquid respectively to or from the ventricle. The 

 liquid enters or leaves the valve-tube through a 

 hole covered by a rubber valve-flap, not shown in 

 Fig. 68. Each valve is surrounded by a glass tube 

 through which the working of the valve may be 

 inspected. 



Mercury manometers measure the pressure in the 

 arteries and veins near the capillary resistance. The 

 arterial manometer is provided with a glass thistle- 

 tube to catch any mercury that may be driven out by 

 a careless operator. 



If the arterial mercury manometer be replaced by a 

 membrane manometer, or if it be provided with a float 

 and writing point arterial-pressure curves may be writ- 

 ten, identical with those obtained from the carotid 

 artery of the dog. 



