296 PRACTICAL PHYSIOLOGY. [LXII. 



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. 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 U -piece. 

 Work the pump about forty 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 intermit- 

 tent 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. 



(b.) Elastic Tube. Clamp off the glass tube near the U-piece, 

 and unclamp the flexible one so as to have no resistance at its out- 

 flow end. Work the pump ; the outflow takes place in jets cor- 

 responding 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 each beat a 

 pulse-beat is felt. The resistance at the periphery brings the 

 elasticity of the tube into play between the beats, and thus con- 

 verts the interrupted into a uniform flow. This apparatus serves 

 also to demonstrate why there is no pulse in the capillaries, -and 

 under what circumstances a pulse is propagated into the capillaries 

 and veins. 



2. Velocity of the Pulse-Wave. 



(a.) Take 3 metres of india-rubber tubing 6 mm. in diameter. To one end 

 of the tube attach the ball of a Higginson's syringe (elastic pump) to imitate 

 the heart, while the other end of the tube is left open, with a clamp lightly 

 fixed on it. Arrange to pump water through the tube. Arrange two light 

 levers on one stand, and place a part of the tube near the pump under the 

 lower lever, and resting on a suitable support, while part of the tube near 

 the outflow end is similarly arranged under the upper lever. Regulate the 

 pressure of the lever upon the tube by means of lead weights. 



(&.) Arrange on the same stand a Despretz's chronograph to record the 

 vibrations of an electro-tuning-fork (30 or 50 D.V. per second), with the 

 writing points of the two levers and chronograph writing upon the drum in 

 the same vertical line. 



