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EXPERIMENTAL PHYSIOLOGY 



also examine the tracings obtained from other animals, such as those, 

 for instance, in figs. 139 and 156. In fig. 135 it is seen that there are 

 two distinct series of undulations on the blood-pressure curve — one a 

 small undulation, due to the heart beat, and the second a larger and 

 slower undulation, which is synchronous with respiration. In an 

 animal, such as the rabbit, in which the heart beats very quickly the 



Fig. 135. — Tracing of the Blood Pressure from a Babbit taken by the Mer- 

 cury Manometer. resp n , Eecord of the Respiration ; b.p., of the Blood 

 Pressure. The Horizontal Line at the Base shows the Position of the 

 Zero of Pressure. Time Tracing in Seconds. 



oscillations due to the heart beat are small, not, as we shall see, 

 because the variation in total pressure with each beat is small, but 

 because the mercury manometer possesses so much inertia that it is 

 unable to respond to variations which are carried out so rapidly. 



