THE MAIN FACTS OF THE CIRCULATION. 



147 



nearly to the base line ; no mean arterial pressure, or very little, is established. 

 The contents of the ventricle (syringe) thrown into the arterial system dis- 



FIG. 42. 



Arterial Scheme : P, unshaded, is an elastic tube to represent the arterial system, branching 

 at .AT and Y, and ending in the region of peripheral resistance, including the capillaries, which 

 are imitated by filling loosely with small pieces of sponge the parts shown as dilated in the figure. 

 The capillaries are gathered up into the venous system, shaded, which terminates at 0. Water is 

 d riven into the arterial system at P by means of an elastic bag syringe or any other form of pump. 

 Clamps are placed on the undilated tubes, c, c', c". When these clamps are tightened, the only 

 access for the water from the arterial to the venous side is through the dilated parts filled with 

 sponge, which offers a considerable resistance to the flow of fluid through them. When the 

 clamps are unloosed the fluid passes, with much less resistance, through the undilated tubes. 

 Thus, by tightening or loosening the clamps the "peripheral" resistance may be increased or 

 diminished at pleasure. 



At A, on the arterial side, and at V, on the venous side, manometers can be attached. At a 

 and v (and also at x and y), by means of clamps, the flow of fluid from an artery and from a vein, 

 under various conditions, may be observed. At Sa, S'a, and Sv, sphygmographs may be applied. 



tend it, but the passage through the peripheral region is so free that an equal 

 quantity of fluid passes through to the veins immediately, and hence the 



FIG. 43. 



Tracings taken from an Artificial Scheme, with the Peripheral Resistance Slight : A, arterial ; 

 V, venous manometer. This figure, to save space, is on a smaller scale than the corresponding 

 Fig. 44. 



mercury at once falls. But the fluid thus passing easily into the veins dis- 

 tends these too, and the mercury in their manometer rises too, but only to 



