INJECTION OF THE ARTERIES. 65 



next appears ; add more water, and follow it around to its 

 starting-point. A little ink may be poured into one of the 

 funnels, and traced around, as the heart is worked, to its 

 starting-point. 



That there is no direct connection between the two halves 

 of the heart may be shown by letting the liquid from each 

 artery empty into the funnel connected with the auricle of the 

 same side of the heart. Different-colored liquids may be used 

 in the two funnels. 



In order to illustrate more fully how the heart is com- 

 posed of two pumps fastened together, and each pumping its 

 own stream, but worked by the same power, try the fol- 

 lowing : 



Take the two funnels supported as in the preceding experi- 

 ment ; connect each funnel with the supply tube of a common 

 bulb syringe ; connect the delivery tubes with the bent tubes 

 used with the heart. 



1. Let each bent tube empty into the funnel from which 

 it gets its supply. There are now two distinct circuits. 



2. Now cross the delivery tubes so that each discharges 

 into the funnel from which the other gets its supply. Now, 

 on working the bulbs, we have a circuit like a figure 8, really 

 one circuit, but the two streams cross each other. 



3. Again, place the two bulbs side by side, and work the 

 two with one hand. 



4. Wrap a cloth around the two bulbs, so that what is con- 

 tained in the cloth cannot be seen. We have now a structure 

 like the heart, but we know its structure. We know that it 

 consists of two pumps wrapped together and working to- 

 gether ; that is, by the same stroke, but with two wholly inde- 

 pendent currents. 



Reason for Injecting the Arteries. The arteries and 

 veins, unless distended with blood, are so nearly of the same 



