BLOOD VESSELS. CIRCULATION 85 



2. Introduce into the open mouth of the glass tube a 

 fine nozzle, so as to offer considerable resistance to the 

 outflow of fluid. Work the pump with the same force and 

 frequency as before. The outflow will still be intermit- 

 tent though less fluid will issue from, and consequently 

 less enter into, the tube at each stroke. 



3. Clamp the proximal end of the glass tube and un- 

 clamp the elastic tube. Let the distal end of the latter 

 be quite open. Work the pump as before. There being 

 little resistance to the outflow, the elasticity of the tube 

 is not called into play, and consequently the flow will 

 be, as in the case of the glass tube, intermittent. 



4. Working the pump as before, insert the fine nozzle 

 into the open mouth of the tube. Considerable resist- 

 ance will now be offered to the outflow of fluid, the elas- 

 ticity of the walls of the tube will be called into play, and 

 the water will issue from the end of the tube in a con- 

 tinuous instead of an intermittent stream. If the tube 

 be sufficiently long and sufficiently elastic in proportion 

 to the force and frequency of the strokes, the flow will 

 be uniform as well as continuous. 



B. MAJOR ARTERIAL SCHEME. 



The pump, P, driven by a motor represents the left 

 ventricle of the heart. It is filled from the rubber bag, 

 B, which represents the left auricle. The valve A.V. 

 represents the left auriculo- ventricular valve, and the 

 valve 8.V. the semilunar valve. The rubber tube A re- 

 presents the arteries, it passes in a coil of about 20 feet 

 through the vessel PL and thence through alternative 

 tubes a, 6, c, d stuffed with sponge representing the ca- 

 pillaries, .into a broad vessel F representing the vein. 



