THE SCHEMA 159 



end of the float is provided with a horizontal arm acting as a writing 

 point, and thus the variations in the level of the surface of mercury 

 can be recorded upon a moving surface. The other limb of the U is 

 placed in communication with the interior of the tube t by means of 

 a glass T-piece. One of these manometers is placed on the tubing t 

 near to the syringe s, the other at the end of the tubing, which termi- 

 nates in two branches, one passing through a short piece of tubing 

 which can be blocked by the screw clamp c ; the other passes to a 

 piece of glass tubing, g, whose centre is tightly packed with glass 

 wool. The two branches then reunite and are connected to a third 

 manometer, m 3 , which latter is in its turn connected to the syringe s 

 by the rubber-tube d. This last piece of tubing is of wider bore and 

 its walls are thin so that it may represent the veins. In using the 

 apparatus the three manometers are arranged to write their move- 

 ments vertically over each other on a recording surface. By this 

 apparatus we are able to study the changes in pressure as we vary 

 the conditions of the experiment. 



Experiment 1. — First fill the schema with water by disconnecting at 

 v 2 and placing both orifices under water. By pmnping the syringe, water is 

 then driven through the tubes until all the air is displaced. The tube d is 

 then compressed and a little more water forced in until the level of the 

 mercury in the free limbs of the manometers lies about 2 cms. above that 

 of the other limb. The tube d is then reconnected to the syringe. The 

 experiment may now be carried out in the following way : (a) Leave the 

 clip c open, when we shall be studying the flow along a closed system of 

 elastic tubes of wide bore and consequently offering but little resistance at 

 each point. Now imitate the beating of the heart by rhythmically com- 

 pressing the syringe s, at first slowly and then gradually increasing the 

 rate of the rhythm. 



On studying the tracings obtained the following points can be 

 made out : — 



(1) The manometer m 1 begins to rise a little earlier than the 

 manometer m' 2 , but later than the instant at which more fluid is forced 

 into the tube from the syringe. 



(2) The amplitude of the movement of the second manometer is 

 rather less than that of the first. 



(3) The movements of the third manometer m 3 are practically the 

 same as those of the other two. 



(4) There is no marked permanent excess of pressure at any 

 point of the system over that at any other point. 



(5) The effect of the filling (the diastole) of the syringe varies 

 according to the rate at which it is allowed to fill. If the syringe be 

 thick-walled so that it possesses considerable elastic recoil, as soon as 

 it is let free it rapidly dilates and sucks in fluid from the tube d, thus 

 setting up a lower pressure in that tube, which diminution of pressure 



