LABORATORY MANUAL OF PHYSIOLOGY. 



creased by loosening the clamps. Tightening the screws would 

 imitate arterial constriction. Loosening them would correspond 

 to a vaso-dilatation. 



Before using the artificial schema, make out the following points. 

 Connect the syringe with a long piece of glass tubing. When the 

 syringe is filled, squeezing it with the hand will force fluid out 

 through the glass tube. Release of the bulb will cause it to fill 

 from the vessel in which the inlet tube is dipped. Press the bulb of 

 the filled syringe with the hand. Note that water is forced through 

 the glass tube and out of its free end in a jet which ceases as soon 

 as the pumping force behind stops. Squeeze the bulb a number 

 of times in succession. Note that there is no flow from the tube 

 between pumps. In vessels with inelastic walls all the force of the 

 pump is exerted in moving the column of fluid forward and in 

 overcoming friction. The friction is inversely proportional to the 

 size of the tube. The smaller the tube, the greater the friction. 

 The longer the tube, the greater the friction. 



For the glass tube, substitute a long rubber tube of small calibre. 

 Press the syringe bulb a number of times in rapid succession. The 

 water will still spurt from the open end of the tubing with each 

 stroke of the pump, but there will probably be some flow between 

 strokes. This may be increased and the flow during the stroke of 

 the pump decreased by partly clamping the tube near the free 

 end. In other words, the peripheral resistance has been increased. 



If the peripheral resistance is sufficiently increased the flow be- 

 comes continuous. With elastic tubes and a high resistance to 

 overcome, part of the force of the pump is expended in distending 

 the walls of the elastic vessel. When the distending force has 

 ceased, the elastic w r alls rebound and force the stored-up fluid on. 

 With each stroke of the pump, then, in a system of elastic vessels 

 some of the energy becomes latent in the distended walls of the 

 vessels, to be transformed into kinetic energy in the interval be- 

 tween pumps. 



With the clamps of the circulation schema open, press the sy- 

 ringe bulb a number of times in slow succession. Note the charac- 



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