100 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



compress the rubber bulb are stored in the wall of the tubing in the 

 form of elastic tension. As soon as the internal pressure is lessened 

 during the interims this elastic power acts upon the water within the 

 tubing and continues to force it onward through the outlet. To ac- 

 complish this end the tubing must be highly distended, i. e., it must be 



FIG. 61. SIMPLE SCHEMA TO ILLUSTRATE THE FACTORS PRODUCING A CONSTANT HEAD 



OF PRESSURE IN THE ARTERIAL SYSTEM. 



o, A syringe bulb with valves, representing the heart; 6, glass tube with fine point 

 representing a path with resistance alone, but no extensibility (the outflow is in spurts 

 synchronous with the strokes of the pump); c, outflow with resistance and also extensible 

 and elastic walls represented by the large rubber bag, e, the outflow is a steady stream due 

 to the elastic recoil of the distended bag, e. (Howell.); 



retained in a condition of hyperfilling. To what constituents of the 

 vascular system may the different parts of this apparatus be compared? 

 Remove the narrow glass cannula (capillaries) from the end of the 

 band-tubing (arteries). This decreases the peripheral resistance. What 

 effects do you observe? Insert a narrow glass cannula and note the 

 effects of this increase in the peripheral resistance upon the distention 



FIG. 62. ARTIFICIAL SCHEMA OF THE CIRCULATION. (Porter.) 



of the band-tubing and the escape of water. In the latter case you may 

 materially decrease the number of the compressions without destroying 

 the constancy of the flow. 



3. Schema of the Circulation. The basin of water represents the 

 left auricle, the rubber bulb the left ventricle, and the large rubber tube 

 the aorta. The large glass tube next to the basin contains the mitral 



