238 EXPERIMENTAL PHYSIOLOGY. 



than the one from the lever near the outflow. Make two 

 ordinates to intersect the three tracings, one where the lower 

 pulse curve rises from the abscissa, and the other where 

 the upper curve begins. Count the number of D.V. of the 

 tuning-fork between these lines. Measure the length of the 

 tube between the two levers, and from these data it is easy 

 to calculate the velocity of the pulse-wave in feet per second. 



2. Rigid and Elastic Tubes. To the vertical stem of a glass 

 T-tube or three-way tube 1 cm. in diameter, fix an elastic 

 pump whose opposite end dips into a vessel of water. To the 

 other slightly curved ends of the tube, fix a glass tube 90 cm. 

 or thereby in length, and to the open end of the tube attach a 

 small short piece of india-rubber tubing with a clamp over it. 

 To the other limb attach an india-rubber tube of the same 

 diameter and length as the glass tube, and fix a clamp over its 

 outflow end. Arrange to pump water through the system. 

 The pump may be compressed directly by the hand, or it 

 may be placed between the two blades of a " lemon-squeezer," 

 and the extent of the excursion of the latter regulated by a 

 screw. 



(a.) Rigid Tube. Clamp off the elastic tube near the 

 T-piece. Work the pump about 40 beats per minute, and 

 force water into the glass tube. The water flows out in jets 

 in an intermittent stream corresponding to each beat. 

 Gradually clamp the outflow tube, and keep pumping, the 

 water still flows out in an intermittent stream, and no 

 amount of diminution of the outflow orifice will convert it 

 into a continuous stream; as much water flows out as is 

 forced in. All that happens is, that less flows out and, of 

 course, less enters the tube. Instead of the clamp at the 

 outflow, a tube drawn to a fine point may be inserted. 



(6.) Elastic Tube. Clamp off the glass tube near the 

 T-piece, and unclamp the flexible one so as to have no 

 resistance at its outflow end. Work the pump, the outflow 

 takes place in jets corresponding to each beat of the pump. 

 Pump as rapidly as possible, and the outflow stream will 

 still be intermittent. While pumping, gradually clamp the 

 tube at its outflow so as to introduce resistance there to 

 represent the resistance in the small arterioles and when 

 there is sufficient resistance at the outflow, the stream 

 becomes a uniform and continuous one. Feel the tube; with 



