160 EXPERIMENTAL PHYSIOLOGY 



travels as a negative wave backwards along the system, affecting first 

 the manometer m 3 , and later m 2 and m 1 . The effect upon the mano- 

 meters is greater the thicker the walls of the tube D, and may be 

 made quite small by increasing the length of that tube and diminish- 

 in» its thickness. It is also decreased by choosing a syringe which 

 does not dilate rapidly. 



In this part of the experiment practically the whole of the fluid 

 travels through the piece of wide tubing c. 



(b) In the second half of the experiment, vary the conditions by inter- 

 posing a high resistance to the flow at one point. This is attained by closing 

 the tube c by the clip, when the whole of the fluid must then pass through 

 the glass tube a, which being packed tightly with glass-wool divides up the 

 stream into a great number of minute channels, resembling capillaries, and 

 thus offers a great resistance to the flow. As before, pump fluid through the 

 system, when the following results will be obtained : — 



(1) With each systole of the syringe the manometers m 1 and m 2 

 will record a rise of pressure as in the former case, but this sudden 

 rise will be absent from the record of manometer m 3 . 



(2) By the diastole the manometer m 3 will alone be affected. 



(3) If only one emptying of the syringe be carried out after the 

 oscillations have ceased, the manometers m 1 and m 2 stand at a higher 

 level than m 3 , and only slowly fall, while m 3 rises until the pressure 

 is once more uniformly distributed. 



(4) If, before the pressure becomes thus equalised, the syringe be 

 once more emptied, the manometers M 1 and m 2 record a further rise 

 of pressure, i.e. a summation of effect has taken place, which is further 

 increased by a third emptying of the syringe, and so on. 



(5) If the emptying of the syringe be continued at a definite rate, 

 at last a condition is reached at which the pressures recorded in the 

 arterial manometers m 1 and m 2 , instead of continuing to rise, oscillate 

 about a mean pressure. The maintenance of pressure at a mean 

 height means that this pressure is just sufficient to force out through 

 the peripheral resistance during the time of one complete cycle 

 exactly the same volume of fluid as is emptied into the arterial tube 

 at each contraction of the syringe. If the movements of m 3 during 

 this time be next studied, it is found that the only sudden variations 

 are the negative waves caused by the active recoil of the syringe as 

 it returns to its original shape. These rhythmic diminutions in 

 pressure do not travel through the high resistance at G, and there- 

 fore do not make themselves felt in the other two manometers. If 

 the emptying of the syringe be repeated sufficiently rapidly, it is 

 found that the mean pressure recorded by the third manometer falls 

 below zero pressure, and takes a negative value. If the movements 

 of the third manometer be not too much masked by these negative 



