156 THE CIRCULATION OF THE BLOOD 



b) Mitral valve: Tie glass window into left auricle and 

 watch appearance of mitral valve as ventricle is squeezed and 

 released. 



c) Mitral and tricuspid valves: Cut auricles away, taking 

 great care not to injure valves. Hold ventricles apex down, 

 and pour water into them from pitcher held about a foot above. 

 Note movement of valves. 



Cut cords attached to edge of one mitral valve and repeat. 



3) Effect of elasticity of blood-vessels and of change in 

 resistance of arterioles: Take bulb syringe * and fit outflow tube 

 to receive both a piece of glass tubing about 2 ft. long and a 

 piece of sap tubing ; also prepare nozzle with a hole about ^r 

 in. in diameter, which is fitted to distal ends of glass and sap 

 tubes. 



a) Put intake tube of syringe into a basin of water, fill 

 syringe, and attach glass tube. Squeeze and release bulb every 

 2 seconds, noting character of outflow. 



b) Attach nozzle to end of glass tube, pump regularly as 

 before, and note character of outflow. 



c) Remove glass tube and attach sap tube. Pump as before, 

 and note character of outflow. 



d) Attach nozzle to sap tube and test as in b). Compare d 

 with a, b, and c, and determine factors contributing to uniform 

 flow. 



1 Instead of this, the more elaborate circulation scheme of Prof. 

 W. T. Porter may be used. It is obtainable from the Harvard 

 Apparatus Co., Medfield, Mass. 



